Sunday, April 15, 2018

Survival Weapons: The AR-15 and Its Derivatives

     
Colt AR-15 Sporter SP1 Carbine (Source)

        This is my fourth article in a series looking at some of the more common weapons recommended for survivalists and preppers. My three prior articles were on the SKSAK style weapons, and the Ruger Mini-14. This article is about the ArmaLite Rifle (AR) 15 system of rifles and carbines. As originally designed, the AR15 rifle was a select-fire weapon using a direct-impingement gas system to cycle the action. Obviously, due to current gun laws, AR style weapons manufactured for civilian sale are semi-automatic only and, in fact, can only accept a semi-automatic fire control group.

        Besides serving as the United State's primary combat rifle for the last 50+ years (as the select fire M-16 rifle and M-4 carbine), in its semi-automatic form, the rifle has become one of the most popular sporting and self defense rifles in the United States, available in an almost endless number of variants and several calibers. However, the rifle was originally designed to fire the .223 Remington caliber cartridge and its updated version, the 5.56x45mm NATO ("5.56"). Since then, the system has been adapted to shoot a variety of different cartridges. This article will focus primarily on the 5.56/.223 weapon.

History:

       To understand the history of the AR 15, I think the best starting point is actually taking a few steps back and begin with the development of the M-1 rifle (the Garand) and early research on the effectiveness of different calibers.

        Following World War I, the Army Ordnance Department reluctantly recognized the need for a combat arm that would allow more rapid fire and reloading than the bolt-action rifles in use by all major combatants in the World War. The initial effort was spear-headed by John D. Pedersen. Pedersen who, as most of you know, had developed a "device" that could be attached to the Springfield M-1903 rifles, allowing for semi-automatic fire of a proprietary pistol sized .30 caliber cartridge. However, before the Pedersen device could be developed in large numbers, the Armistice was signed and World War I ended. Ordnance recognized the potential usefulness of a semi-automatic, high capacity weapon, but also (correctly) noted that the cartridges intended for use in the Pedersen device were woefully under powered for the battle field. Pedersen's solution was to develop both a new cartridge and a new rifle. After deliberation, Pedersen came up with .276 caliber, 125-grain cartridge that was half an inch shorter than the .30-06 in then-current use. Pedersen claimed that the cartridge would be more lethal than .30-06, with with half the recoil and 20% less weight. The army put together a board (the "Pig Board") to conduct tests by shooting pigs. The Pig Board tested three rounds: the .30-06, Pedersen's .276, and a .256 round apparently in use by some European armies. The results of the test showed that at "short range" (300 yards), the .256 caused the most traumatic wounds, followed by the .276, and with the .30-06 coming in last. At 600 yards, however, the performance gap had narrowed. Unfortunately for Pedersen, not only did Ordnance select John C. Garand's design for a new rifle (the M-1 Garand), but because of budgetary issues during the 1930s, elected to stay with the .30-06 rather than change calibers.

       However, World War II and the Korean War both again called into question the need for a high power cartridge. The Soviets and the European powers had been impressed with the German's 7.92×33mm Kurz cartridge used in the Sturmgewehr ("storm" or "assault" rifle) -- the StG 44--and clamored for their own "intermediate" cartridge (i.e., intermediate between handgun cartridges used in submachine guns and full power rifle cartridges). Of course, the Soviets developed and used their 7.62x39mm cartridge. The British lobbied for a .280 caliber weapon, and Fabrique Nationale obliged by developing a rifle to shoot it: the FN FAL. However, the American Army was adamant about sticking with a full-power .30 caliber round, although willing to move to a shorter overall cartridge length. Thus, the decision was made to adopt the 7.62x51mm NATO for all NATO forces (which, in its civilian version, is the .308 Winchester). In conjunction with this, the United States Army also elected to proceed with adopting the M-14 rifle to fire the new round.

         Nevertheless, there continued to be advocates for smaller, faster rounds. Research conducted by the Ballistics Research Laboratories (BRL) since World War II had suggested that velocity played a more significant role in wounding than did mass. In 1952, Donald Hall, a civilian researcher for the BRL published a report entitled The Effectiveness Study of the Infantry Rifle, which concluded that a smaller, higher velocity round than the .30 would be more effective for use on the modern battlefield--that is, more lethal within the typical ranges of engagement. By 1958, BRL would take this research farther and arrive at the conclusion that the best possible bullet would be a .22 caliber 50-grain bullet with a velocity of 3,500 feet per second. Concurrently with Hall's initial report, the Operations Research Office (ORO) also released a report in 1952*, entitled Operational Requirements for an Infantry Hand Weapon (alternative source), that determined that 300 yards was a rifle's effective limit, and the vast majority of lethal hits occurred at under 100 yards. Finally, S.L.A. Marshall's ideas that very few infantry would actually fire their weapons were influential, as well as his solution: advocating mass firepower over marksmanship, suggesting it was better to arm soldiers with automatic weapons rather than precision rifles.** Effective automatic fire virtually necessitated a smaller, lighter recoiling cartridge.

       Of course, any history of the AR-15 would be incomplete without discussing the weapon, itself. After all, we know that the .223 could be used in a more traditional style combat rifle (e.g., the Mini-14). It was the combination of the cartridge with a light weight, modular rifle that gave us the AR-15 weapon system.

       The genesis of the AR-15 begins shortly after World War II with aviation manufacturing expert George Sullivan who believed that the advanced materials developed by the aviation industry, especially in aluminum and plastic, could be used to make a much lighter and better rifle. In 1953, Sullivan shared his ideas of an aluminum rifle to a aircraft manufacturer, Fairchild Engine and Airplane Corporation, and, by 1954, Fairchild had created a firearms subsidiary: ArmaLite. However, ArmaLite's initial forays into manufacturing firearms were certainly innovative, but suffered problems, and Sullivan realized that he needed to bring on board someone with actual knowledge and experience in manufacturing firearms. A chance meeting with Eugene Stoner at a shooting range led to his being hired by ArmaLite as its chief engineer.

       While it would be tempting to say that history was made, it was a rocky start and the AR-15 nearly didn't come to fruition. With Stoner on board, ArmaLite decided to enter the competition for the new .308 caliber select fire rifle intended to replace the M-1 Garand. ArmaLite's entry was the AR-10, which performance exceeded all its competitors in all areas but one: the 6,000 endurance test. To keep the weight down, ArmaLite has used an aluminum barrel shroud with a steel insert, but the insert was too thin. The barrel overheated and deformed. The Army's in-house weapon--the T44--was officially adopted as the M-14.

        While other nations showed interest in the AR-10, there were no significant sales. However, Colonel Henry Nielsen (head of the Army's Infantry Board) and General Willard Wyman (commander in chief of the Continental Army Command) encouraged Sullivan to continue development of the weapon, but with a .22 caliber bullet as suggested by the ORO report. Thus, began the development of the AR-15. With support from Nielsen and Wyman (and to the consternation of the Ordnance board), a test of the AR-15 against the M-14 were conducted. The AR-15 outperformed the M-14 in reliability generally, but some shenanigans by the Ordnance board resulted in it failing the arctic (cold weather) test. About the same time, Nielsen and Wyman retired. With the chance of a U.S. Army contract dead, Fairchild sold ArmaLite to Colt, who then attempted (unsuccessfully) to market the arm. Things were looking dire for the weapon when Colt had the opportunity to demonstrate it for Air Force General Curtis LeMay. LeMay loved the weapon, and decided that he wanted it for the guards at the Air Force's Strategic Air Command (SAC) bases. However, even that was frustrated when the Defense Department turned down LeMay's request to purchase AR-15s.

        Just as the AR-15 was on death's door, however, it caught the attention of yet another department: the relatively new Advanced Research Projects Agency (ARPA, now the Defense Advanced Research Projects Agency, or DARPA), who had been tasked to develop technological solutions to deal with guerrilla warfare. ARPA purchased a small number of the new rifles to give to U.S. military advisers in Vietnam for testing. Initial testing in 1961 resulted in enough enthusiasm with the new weapon and cartridge that ARPA ordered an additional 1,000 weapons for broader field testing in 1962.

        The results were impressive, to say the least, and appeared to support Hall's and the ORO's determination. As Alexander Rose recounts in his book, there was significant support for the new weapon by those that tested it. "[N]one of these hard-bitten veterans in Vietnam had ever before witnessed the kinds of devastating wounds inflicted by the AR-15; none had thought such lethality possible in a rifle, particularly one firing a 'varmint' round like the .223." Rose also notes that the photographs of the victims from this test remained classified until the 1980s because the wounds were so horrendous. Rose lists descriptions of the wounding effects reported by the testers, which are really quite gruesome; one, for instance, reported that "[a]t a distance of approximately 15 meters, one Ranger fired an AR-15 full automatic hitting one VC with 3 rounds with the first burst. One round in the head took it completely off. Another in the right arm, took it completely off, too. One round hit him in the right side, causing a hole about 5 inches in diameter." (Rose 373-74).

       Unfortunately, the later range testing of the weapon could not reproduce these wounds. The reason is that although Stoner had specified a 1:14 twist for the new weapon, Colt's test models went out with rifles with a 1:16 or 1:18 twist. This made the bullet very unstable. Nevertheless, the debate attracted the attention of Secretary of Defense McNamara, who despised the Ordnance department because of the expense of the development of the M-14 and its initial production and performance problems. In 1962, McNamara abolished the Army Ordnance by combining with other technical agencies into a Material Command. He also ordered another analysis--a more scientific analysis--of which was a better weapon. The analysis came back in favor of the AR-15. Nevertheless, the Army still objected to having to adopt a new rifle when they had just barely adopted the M-14. McNamara decided to split the baby, allocating funds for a limited purchase of AR-15 (now the M-16) rifles for the Air Force and or Army troops in Vietnam, but had also suspended manufacture of the M-14. The tide had turned. And when the Vietnam war subsequently ballooned, it spelled the death knell of the M-14.

        The M-16 would go undergo further refinement while in the service of the Army and Marines, including, eventually, the adoption of a heavier bullet and even faster twist rates to stabilize these bullets. Nevertheless, after the expiration of the 1994 assault weapons ban, considerable innovation and improvement has come with input both from the military and civilian shooters.

       As far as I can tell, Colt started selling a semi-automatic only version of the AR-15 to the general public in 1963, prior to it obtaining any significant military contracts. Initially Colt referred to its civilian version as the AR-15 Sporter. (The AR-15 Sporter sold for about $189.50 MSRP at the time of its introduction, or approximately $1,480 in 2016). But after the military adopted the M-16, Colt started calling its military rifle the CAR (Colt Automatic Rifle) 15, and re-designated the Sporter as the SP-1. One source I came across indicated that the Colt had manufactured (and presumably sold) 200,000 SP-1s by 1985.

    According to a detailed time-line of the AR 15 at AmmoLand, in 1989, "Jim Glazier and Karl Lewis of Lewis Machine and Tool Company (LMT), operating a new entity called Eagle Arms, begin producing complete AR-15 rifles for the consumer market. By this time, many of the earlier AR 15 Rifle related patents had expired, thereby opening up the market for complete AR-15 type rifles." This was, in many ways, a watershed moment because, with the expiration of the Colt patents, it opened up manufacture of  AR rifles and carbines, and their parts, to competition, spurring lower prices and innovation.

       I would suggest that the next watershed moment for the AR was the 1994 Assault Weapons Ban. I've noted in other posts that the AR, while popular within limited segments of the firearms market, was not a particularly popular weapon overall in the 1980s and early 1990s. I suspect that most gun owners were probably not aware of the availability of the AR in the 1980s, or, at least, had probably never considered owning one. But, in a classic case of unintended consequences, the Assault Weapons Ban suddenly catapulted the AR (and other defensive rifles) into the consciousness of the gun owning public, and everyone suddenly wanted one. Although the rifle continued to be manufactured in a neutered form throughout the period of the ban, the expiration of the ban, concurrent with veterans returning from overseas conflicts, propelled the AR to one of the best selling firearms on the market. Subsequent threats to ban or regulate the weapons continued to drive high sales throughout the last decade. I suspect that the popularity of "first person shooter" video games will continue the popularity of the AR and other modern sporting rifles.




M16A1 (source)














Specifications: 

       The specifications for civilian versions of the AR vary considerably depending on the specific barrel length and other features. However, the specifications for the military versions of the AR should give you a good approximation of what you would see in a comparably sized civilian weapon. The specifications for the Vietnam era M-16A1 Rifle (see photograph above) are as follows:
  • Weight (unloaded): 7 lbs (3.18 kg)
  • Length: 39.5 in. (990 mm.)
  • Barrel length: 20 in. (508 mm);  21 in. (533 mm.) with flash suppressor
  • Operation: Gas, direct impingement.
In 1983, the Army began to replace the A1 models with the A2. Major differences were a heavier (i.e., thicker walled) barrel with a 1:9 twist (later 1:7), an improved rear sight capable of adjustment for both windage and range, burst fire rather than full auto, a sturdier round handguard, and a sturdier stock. The specifications for the M16A2 are as follows:

  • Weight (with loaded magazine):  8.79 lbs (3.99 kg)
  • Weight (unloaded): 7.5 lbs. (3.4 kg)
  • Length: 39.6 inches (1000 mm)
The M-16A3 was introduced in 1994, but is essentially identical to the A2 except that it offered true full automatic fire instead of burst fire. It was never adopted for general use. However, in 1998, the Marine Corps adopted the M16A4. The major differences were that it went back to the burst fire over full automatic, and it offered a flat top receiver with a Picatinny rail for the mounting of optics and, subsequently, sported the quad-rail hand guard allowing other accessories to be added.

       In 1994, the M-4 carbine began to be introduced. Although initially intended as a weapon for officers and specialists, its light weight and handiness made it extremely popular with troops, and it has replaced the M16A2 as a general issue weapon. The specifications for the M-4 Carbine are as follows:
  • Weight (unloaded): 6.5 lbs (2.9 kg)
  • Length: 33 in. (840 mm.) with the stock extended.
  • Barrel length: 14.5 in. (370 mm).
Obviously, weapons with heavier barrels, billet receivers, and/or quad-Picatinny rails will weigh more. And optics and other accessories can add to the weight, sometimes substantially.

       Just for comparison, the standard Ruger AR 556 (sporting an adjustable stock, milspec front handguard, and a 16 inch barrel) weighs in at 6.5 lbs. A Daniel Defense "Ambush" in 5.56 mm (sporting an adjustable stock, 18 inch barrel, MLok handguard with a monolithic Picatinny rail) is listed as weighing 7.0 lbs. So, it would be fair to say most ARs will fall within the 6.5 lbs to 7.5 lbs range (unloaded), without counting optics and other accessories.

Notable Characteristics

        The AR offers several advantages over other semi-automatic rifle designs. First, although more important for larger calibers than 5.56/.223, is the straight (in-line) lay out of the barrel, receiver, stock, which allows for greater control over recoil (which can be further reduced by an appropriate muzzle device). Second, unlike competing designs, the AR uses a solid, machined receiver of aluminum, giving it light weight without sacrificing stiffness necessary for accuracy. Most other semi-automatic rifles either use a light weight stamped sheet metal receiver, which lack in stiffness, or heavy milled steel receivers. Third, the bolt is completely enclosed and the dust cover effectively seals the interior of the rifle from dust, mud, etc. In fact, the AR is superior to all its competitors (including the AK) in reliability in the infamous mud and dirt tests you see on many YouTube channels. (The direct impingement system also assists in this as the ported gas tends to blow debris out of the action). Fourth, the rifle is of a modular construction that allows its customization and upgrades. Fifth, with modern designs incorporating rail systems, it is easy to attach optics or other accessories.

       The modular construction on the AR is worth a bit more discussion. One of Stoner's goals with the weapon was to make it easy to clean the weapon. To do that, he used two receivers (an upper and lower) that were attached by two easily removed pins. Cleaning is performed by removing the rear pin and, with the front pin acting as a hinge, tilting the rear of the receiver up allowing easy access to the barrel, easy removal of the bolt carrier, and access to the trigger group. This was not something unique to the AR; other weapons had made use of this arrangement including, for instance, the HK G3 and its descendants. However, whether it was intended or not, Armelite or Colt made a decision that was of potentially immense consequence to shooters, and which distinguish the AR from the G3 design: the lower receiver was the part of the weapon to receive the serial number.

       As most of you know, U.S. law requires every firearm have a serial number. But, for these purposes, the "firearm" is the frame or receiver of the firearm which is serialized. In the case of the AR, the lower receiver became the serialized part. Compare this to the G3 and its variants which also make use of an upper and lower receiver. In the case of the G3, however, the upper receiver was chosen for the serialized part. The consequence of this is that the whole barrel and upper receiver of the AR can be swapped out with another upper, possibly of different barrel lengths or even calibers, without having to purchase that upper through a licensed firearm dealer (FFL).

        For most of the history of the AR, the ability to easily swap uppers was probably not something of any real significance. However, the last decade has seen several serious attempts to develop calibers that are compatible with the standard AR 15 lower, but offer certain other advantages; calibers including the .300 Blackout, .458 Socom, .450 Bushmaster, .22 Nosler, 6.8 SPC, 6.5 Grendel, and so forth. A current shooter has the option of seriously changing the basic characteristic--the caliber and barrel length--of his weapon without having to buy a new weapon. Thus, for instance, a person could in theory have a single lower that, by switching the upper, could convert his rifle from a short barrel carbine suitable to home defense, to a large caliber rifle capable of taking large game at short range, to a longer barreled weapon capable of being used for long distance shooting. And all without having to learn a different manual of arms for each; and taking advantage of the best trigger you can afford without having to upgrade the trigger on multiple rifles. Having said all of that, though, I'll also acknowledge that I don't know anyone that actually uses multiple uppers with a single lower receiver; at least, not that I've noticed. So this may not be as significant of a feature as generally touted.

       The straight layout and direct impingement system also required a straight buffer tube attached to the back of the lower receiver. While probably not apparent with the original AR, the consequence today is that it is very easy to swap stocks between weapons using a carbine, multi-position, buffer tube.

       Because the barrel is attached via a large barrel nut, rather than being screwed in or pinned into place like many other rifles, it is relatively easy for even a hobbyist to remove or install the barrel. The use of a barrel nut has also made it easy for various manufacturers to design and produce modified barrel nuts that accept the mounting of free floated hand guards allowing better accuracy and further customization options.

      However, I believe that the development most significant to preppers was the incorporation of the Picatinny rail systems to common receivers, allowing the easy mounting of optics. When these rail systems were added to the hand guards (the well known, albeit heavy, quad rail systems), it allowed easy attachment of a multitude of accessories such as flashlights, lasers, forward grips, etc., without recourse to proprietary (and expensive) mounting systems. And although the quad rail has fallen out of favor due to its size and weight, the M-Lok and K-Mod systems on free-float hand guards still allows the same level of customization. If you have an older rifle or carbine sporting a quad-rail system, I would strongly encourage you to look at a newer M-Lok hand guard in order to save weight and provide a slimmer profile that is easier to grip.

       Another point, and something I raised in my discussion of the Mini-14, is that with so many different manufacturers and parts distributors, you can easily obtain parts for the AR. So, if something should brake or wear out, you could repair or replace it. Certainly, it would be worth putting together an extra set of springs, firing pin, o-ring for the extractor, etc.

General Handling and Thoughts

        To be forthright, I was not a big fan of the AR when I was younger because of the experiences I had with poor reliability when using other people's ARs. Also, used as I was to standard types of bolt-action and semi-automatic rifles, it was awkward to manipulate the charging handle and get used to a bolt release on the left side of the rifle. It was a long time before I decided to go the AR route, and the reason I finally did so was because of the ease of mounting optics or other accessories to it compared to the AK or Mini-14.

       However, now that I'm used to its operation and layout, I will admit that the AR has earned its place as the most popular defensive rifle in the United States. Although I still think the Mini-14 is superior for snap shooting--mostly because of the low sight to bore axis and the standard rifle stock--the AR is definitely quick and easy to use. It can be front heavy with a long, heavy barrel. But shorter barrels, such as the 16 inch, balance pretty well. The old mil-spec iron sights are superior to the iron sights of any other defensive or combat rifle in current use; and the ease of mounting optics on the current "flat top" receivers is superb.

       The reliability of the AR can be excellent with good parts; but there may be some fine tuning involved, especially if you assemble your own. On the other hand, I think the rifle is maintenance intensive because of the direct impingement system. That is, the cleaning of the BCG and receiver takes more time than many other designs where you can get away with wiping down the bolt face and swabbing out the chamber and barrel. Also, although I have not seen it first hand, it is my understanding that the hot gases, especially with heavy firing, can affect the temper of springs in the trigger group or for the ejector, requiring replacement. Fortunately, the design of the weapon is such that it is easy to perform that maintenance. Even replacement of the firing pin is easy.

       In short, the AR is equal to or superior to the other common defensive rifles on the market. I will admit that I do not have experience with everything else out there, but I've handled and shot SKS rifles, various versions of the AK, HK and Cetme roller-lock rifles, FAL's, Mini-14's, as well as various civilian semi-automatic rifles and carbines. Perhaps some of the updated AK designs may prove superior in coming years, but only because they have adopted features from the AR.

       With that out of the way, I would like to discuss specific options available for AR style rifles and carbines:

Calibers

       As I noted above, there are a plethora of different calibers for the AR15 platform, including, without limitation, the .223/5.56 (.223 Wylde), .22 Nosler, .224 Valkyrie, 6.5 Grendel, 6.8 SPC, .300 Blackout, .450 Bushmaster, .458 SOCOM, .50 Beowulf, and probably some others that I've missed. However, the 5.56, with an appropriate barrel twist rate, will do 90 percent of what you need from a defensive and survival rifle/carbine, including hunting up to white-tail deer sized game. 5.56 mm ammunition is also widely available at very reasonable prices, and a standard magazine will hold 30 rounds of 5.56--other calibers, with the exception of .300 Blackout, not so much.

Barrels

       Other than caliber, the most basic consideration for an AR rifle is the barrel. Not just barrel length, but twist rate, barrel profile (e.g., heavy barrel, pencil profile, etc.), and barrel material and coatings.

        Barrel Length

       Bullets wound or kill by poking holes in a target that either destroy something vital to survival, and/or cause shock and loss of blood. Obviously, the bigger the hole (both diameter and depth), the more effective the wound at putting down the target. While you can use bullets that simply punch a hole, it is generally better to select a round that magnifies the wounding effect of the bullet used. There are three general methods used to magnify the wounding effects: fragmenting (i.e., the bullet breaks apart), "tumbling" or yawing, and expansion (i.e., mushrooming).

        When discussing rifles calibers, fragmenting bullets, because of their low penetration, are generally reserved for hunting varmints; they are typically not suited for self-defense against a man-sized target.

        Expanding bullets dominate the hunting market because they can be designed to reliably expand over a wide range of velocities. However, most expanding bullets use an exposed lead tip, which are susceptible to damage from rough handling or improper storage, and are not quite as aerodynamic as other types of bullets. Thus, while expanding bullets are ostensibly not used by militaries because they are banned by international law, the reality is that they are generally unsuitable for general military issue.

       Yawing, or tumbling, is when a bullet turns within a target. Most pointed rifle bullets will, if they don't expand or fragment, yaw so that the base of the bullet will proceed the tip (i.e., its orientation changes so that the bullet is traveling base first). The point that a bullet begins to yaw depends on the velocity, caliber, and velocity of the round. For instance, a full metal jacket (FMJ) .30 caliber bullet will generally penetrate quite deeply before it yaws, which is one of the reasons why the Russian 7.62x39 is not an effective man killer (but can be excellent for poaching large game animals).

       The M-16 has historically relied on both yawing and fragmenting. That is, when the bullet yaws, if it is still traveling at a sufficient velocity, it will fragment. This can be influenced by bullet design. So, for instance, the M855A1 round is designed to yaw no more than 3 inches from its impact point.

     However, this yawing is still highly dependent on muzzle velocity. For typical 55 grain FMJ (probably the most popular), this velocity is 2,300 feet per second (fps). The M855 projectile requires at least 2,500 fps. 77 grain BTHP generally needs velocities of 2,100 to 2,200 fps.

      So, how is this related to barrel length? Basically, shorter barrels will give lower muzzle velocities, which translates to lower velocity down range. For example, M855 has a muzzle velocity of 3100 fps out of a 20-inch barrel. That is down to 2900 fps from a 16 inch barrel. At 9 inches, the muzzle velocity is less than the 2500 fps required for yaw and fragmentation. So, if you want better lethality at long ranges, you will want a longer barrel: 18 or 20 inches. If you are okay with trading a little of the long range lethality for mobility, you can get acceptable performance from a 14 inch or 16 inch barrel. And you should avoid shorter barrels--at least for 5.56.

        Twist Rate

       Differing twist rates exist to stabilize different types of bullets. Contrary to popular belief, the necessary twist rate varies according to the length of a bullet, with long-for-caliber bullets requiring a faster twist rate than for standard length or short-for-caliber length bullets. Because most bullets are made from similar materials--copper and lead--long-for-caliber generally translates to weight. That is, heavier bullets will need a faster twist rate. But bullets made from lighter materials (e.g., all copper) will also be long-for-caliber even at lower bullet weights, but will still require a faster twist rate.

       The military originally used a 1:12 twist rate that is suitable for light weight (55 grain or less) bullets. Later, this was changed to 1:9 and then to 1:7 in order to accommodate the tracer rounds (which were long-for-caliber). Common twist rates for civilian rifles are 1:9 (which was, at one time, the most popular, but somewhat uncommon on new manufacture rifles), 1:8 (which is popular for target rifles), and 1:7 (just because that is what the military now uses).

       Typically 1:9 will stabilize bullets in the range of 55-85 grains.

       Typically, 1-8 will stabilize bullets in the range of 50-80 grains.

      Typically, 1-7 will stabilize bullets in the range of 55-85 grains.

However, the lower ranges on these may result in an over stabilized bullet. Thus, for 55 to 62 grain, a 1:9 twist rate may be better than a 1:7. Frankly, most people using an AR in .223 or 5.56 will be better off with 1:9 or 1:8 than the military's 1:7. However, if you think you will be shooting heavier bullets, go with the faster twist rates.

        For some reason I've never been able to determine, certain twist rates seem to be used (or not used) depending on the barrel material. For instance, the standard carbon steel barrels are typically in 1:7 or 1:9, but rare in a 1:8. On the other hand, almost all stainless steel barrels are in 1:8. So, keep that in mind.

       Barrel Profile

       The barrel profile is the outside shape and dimensions of the barrel. AT3 Tactical has a good article on different profiles available for AR rifles, which you can read here. The basic issue in selecting a profile is weight versus a change in point of impact (POI) due to either heat or barrel whip. That is, light weight barrels can quickly heat from repeated firing, which can cause the barrel to warp; and the thinner ("pencil") barrel is more susceptible to barrel whip (distorting of the barrel due to harmonic waves) when fired. Conversely, a heavy barrel weighs a lot, but will minimize POI shifts due to heat or barrel whip.

        If you are going to do a lot of shooting, or want something for target shooting, you probably should go for a heavier barrel profile. For most cases--particularly in a 16 inch or shorter barrel--the M-4 profile offers a good mix of stiffness and light weight.

        One highly regarded barrel profile is the M-4 SOCOM which is a heavier version of the M-4 barrel, but thicker at the magical distance of 4 to 6 inches from the bolt face, where barrels tend to heat the most. This greater thickness appears to reduce barrel warp and whip, making it more accurate than the standard M4 profile.

       Sometimes companies offer thicker barrels with fluting or dimpling to shave off weight while, in theory, maintaining stiffness. Based on my reading, fluting or dimpling can introduce other variables and actually reduce accuracy by aggravating the warping of a barrel when heated. Thus, research this carefully before putting down the extra cash for a fluted or dimpled barrel.

       Barrel Material

        Most AR barrels are either made of Chrome Moly Vanadium (CMV) steel or stainless steel. Military specifications calls for 4150 CMV steel barrels, but you may come across barrels using 4140 CMV steel. 4150 is used for automatic weapons because of its wear characteristics, and ability to handle extreme temperatures (over 700 degrees Fahrenheit). Thus, all other things being equal, a barrel made of 4150 will last longer than a barrel made of 4140.

        416-R stainless steel is also commonly used to make barrels. Because stainless steel is easier to machine and take fine cutting, it is easier to produce a highly accurate barrel using stainless steel. Also, because of the wear characteristics of stainless steel, it will maintain better accuracy over the life of the barrel. Finally, stainless steel is easier to clean and more resistant to corrosion than a bare CMV steel barrel would be--this is generally a moot issue, however, because of coatings available for CMV barrels. The downside of stainless steel is that it does not have the range of temperature use as CMV barrels. That is, high temperatures (such as from sustained or rapid firing) can lead to greater wear and throat erosion, and it is not as amenable to be used in cold weather. It also does not have quite the barrel life as CMV barrels--particularly 4150.

       Occasionally you will also see barrels listed as 41v45 or 41v50. These are steels used for making cold hammered forged barrels.
     
       Most people will never notice the differences between the barrel materials: that is, they won't subject their rifles to the heavy use that would require a 4150 barrel, nor develop the shooting skill to notice the difference between a CMV barrel and a stainless steel barrel. However, since preppers are concerned, in theory, with having to use a weapon in combat, including rapid fire, the balance would favor a barrel made of 4150.

       Coatings and Treatments

       Coatings or treatments are not necessary for stainless steel barrels, although it is becoming more common for these to receive a Nitride treatment (discussed below).

       One of the initial problems with the AR in Vietnam was corrosion in the barrels, which had no coating or lining when the M-16 was first introduced. This was corrected by use of chrome lining (which, I would note, the Soviets had used from the get-go in the AK and SKS weapons). Thus, mil-spec barrels today feature chrome lining. The disadvantage to chrome lining is that it can (but not necessarily) reduce accuracy. Because it is an additional layer of material being applied to the inside of the barrel, chrome line barrels are machined slightly oversized to account for the layer of chrome that will be subsequently added. However, it is difficult to evenly apply the chrome, which is what can produce the reduced accuracy.

       One of the newest treatments for barrels is a Melonite/Nitride/QPQ Salt Bath treatment which chemically changes the surface of the steel rather than applying an overlying material as with chrome lining. In addition, because it is a chemical treatment, the entire barrel (inside and out) can be treated to produce a uniform appearance. This chemical treatment makes the steel "slicker" (i.e., easier to clean), corrosion resistant, and hardens the surface slightly. If you are using a chrome-moly steel barrel, my recommendation is to find one that is Melonite treated.

       Forming of the Lands and Grooves

      There are three methods for forming the lands and grooves of the barrel. One of the most common you will see is called button rifling which uses a carbide die (the "button") forced through a barrel blank to form the lands and grooves. Traditionally, lands and grooves were formed by cutting the grooves with a cutting tool, which would gradually cut the groove deeper with each pass. Finally, cold hammer forged barrels are made with a rifled mandrel against which the barrel blank is worked (hammered) to conform to the pattern on the mandrel.

       All these methods can produce an accurate barrel, depending on the quality and care of the work. However, hammer forging and button forming are more consistent than cutting. Also, hammer forging, because it works the metal, does harden the metal slightly. So, again, if you are interested in maximizing barrel life, hammer forging is probably for you. However, you will generally pay a premium for cold hammer forged barrels.

      Barrel Extension

       The barrel extension is a part that attaches to the rear of the barrel into which the bolt lugs lock. The important point about the extension is to get an extension with M-4 feed ramps cut into it, which ease the feeding of rounds. This make the feeding of cartridges easier, whether a carbine or rifle.

Trigger Group

       The trigger is probably the most important part of the rifle when it comes to accuracy. Standard mil-spec triggers are stiff and rough, and so the trigger will generally be one of the first things that should be upgraded.

       AR triggers are available in both single-stage (no take up before the hammer release) and two-stage (offering take up before the trigger is released). Two-stage is generally preferred for defensive rifles because it is more forgiving of an errant finger resting on the trigger prior to shooting.

       Replacement triggers are also available as a group of trigger parts, or as single-unit drop in. The drop in triggers are easier to install, but they will generally require a set of anti-slip or anti-rotation trigger pins so the pins do not slip out. Also, if there is a malfunction with the trigger group, it is harder to troubleshoot the drop in units.

       The Truth About Guns published an extensive test of drop in triggers in 2016, which reviews the various triggers available at that time. If you are interested in going this route, I would recommend checking out that article.

Receivers

       Mil-spec receivers are made of forged aluminum. However, billet receivers (machined from a block of aluminum) have become increasingly popular. Forged aluminum receivers are lighter and stronger than billet, but billet receivers may offer certain features that you may want (or just look cool). Billet receivers also cost more than forged.

       At one time, you would have had the option of getting an upper receiver with the forged carry handle that is one of the most distinctive features of the M16. However, almost all receivers manufactured today are "flat top" featuring a Picatinny rail for mounting optics. For a survival weapon, there is no reason to get anything but a flat-top receiver, so the lack of upper receivers with carry handles is no loss. In any event, if you want a carry handle, you can find handles that will mount on the Picatinny rail.

Sights

       I may be branded a heretic for saying this, but the era of iron sights is basically over. Given the top Picatinney rails which allow for easy, solid mounting of optics, and the sturdiness of many current optics available for the AR, I would forego iron sights in favor of getting a quality red-dot sight or 1-4, 1-6, or 1-8x variable scope with an illuminated reticle and designed for tactical shooting. Over the last couple of years, I have seen both special forces shooters as well as competitive shooters eschew iron sights--even back up iron sights (BIUS). The advantage to not mounting the iron sights is that you can mount the optic further back, if using a scope; or, if using a red dot, you have room behind the red dot to mount a magnifier. If you get a red dot, be sure to get one that has the extended (20,000+ hours) of battery life so that it can always be on.

Bolt-Carrier Group

       The bolt carrier group (BCG) holds the bolt, firing pin, and moves back and forth to pick up or eject cartridges. Most BCGs are an M16 (full auto) style, but you will also see AR15 (semi auto) bolt carriers which are a little lighter, and even lighter BCGs generally intended for competition. The latter generally require an adjustable gas block or some other way to regulate the gas system to tune the rifle for proper operation. For your purpose as a prepper, I would recommend avoiding light weight BCGs and just go with the standard M16 style.

       The decision that you will generally face in regard to the BCG is the type of coating. Mil-spec calls for a Parkerized (manganese phosphate) coating. More modern coatings are available that have greater wear characteristics and/or lubricity. These include chrome coatings, Melonite treatment, Nickel Boron coatings and titanium nitride coatings. Just for the wear characteristics and corrosion resistance, I would select something other than a Parkerized coating. I like the black (i.e., low profile) color of the Melonite coating.

       Because of the extreme forces on on the bolt, you will want to make sure that the manufacturer has tested it for material defect. These tests are high pressure testing (HPT) and magnetic particle inspection (MPI), and a manufacturer will generally advertise such testing if it has been done.

      Another item to check for is proper staking of the gas key. The gas key is the part of the BCG which is struck by the gas from the gas tube, and drives back the BCG. It is not cast or machined as part of the BCG, but is a separate part screwed into place. If the screws are not correctly staked, the screws can back out, resulting in a gas leak or separation from the BCG.     

Buffer Tube

       The buffer tube contains a buffer and buffer spring that act to retard the backward motion of the BCG as it recoils, and then returns it forward again to pick up a new round and lock into place. Rifle buffer tubes are intended to only be used with fixed rifle stocks. Carbine tubes are designed to take a collapsible/adjustable stock. Pistol tubes lack the ability to mount and lock into place a stock.

       The primary difference is between mil-spec and commercial tubes. The mil-spec tubes are machined so that the threading on the end of the tube is above the level of the rest of the tube, while commercial tubes simply have the threading cut into the tube. Also, the end of the tube is shaped differently. Importantly, stocks designed for a commercial tube will not work with a mil-spec tube, and vice versa. My recommendation is to just stick with a mil-spec tube.

Hand Guards

       The standard mil-spec handguard is a round polymer handguard that serves to protect the gas tube from damage and keep the users hand from getting burned on a hot barrel. For a period of time, aluminum handguards with machined Picatinny rails on all four sides (quad rails) were popular. However, these types of rails are bulky and heavy, and have fallen out of favor. Today, there are a large number of manufacturers that offer free float handguards of one sort or another; most of these offer a Picatinny rail on the top (12 o'clock position) of the handguard, and use either a Key-Mod or M-Lok slots to allow the mounting of sections of Picatinny rails on other locations.

       Free float handguards that allow mounting of Picatinny rails offers a lot of advantages over standard handguards if you are planning on using various accessories such as vertical or angled handgrips, flashlights, lasers, etc. However, they vary in length, cost, and quality. If you choose a free float handguard, be sure to get one that is long enough to extend past the gas block on the barrel in order to protect the gas tube. Also, investigate how solidly the handguard will mount--it is not unknown for cheaper quality tubes to twist.

       If you do go with a free-float handguard, you may consider whether to get one in Key-Mod or M-Lok. M-Lok was developed by Magpul to address shortcomings in the Key-Mod system--namely, that the Key-Mod system would crack polymer components. However, testing has discovered that the M-Lok system is inherently stronger than the Key-Mod system, and, at least from my perspective, it appears that the Key-Mod system is falling out of favor.

Gas Tube Length

        The gas system for the AR comes in various lengths (referring to the location of the gas port and the length of the gas tube). There are 4 lengths: pistol, carbine, mid-length, and rifle. Generally, best operation is when the gas port is located roughly mid-way along the length of the barrel.

        Pistol length systems are used for barrels less than 10 inches--the distance of the gas port from the receiver is 4 inches. As noted above, the 5.56 mm should not be used from short barrels because it lacks the velocity for effective terminal performance.

        The distance from the port to the receiver is 7 inches in a carbine length system. Consequently, they can be used for barrels of 10 to 18 inches.  However, the higher port pressure and sharper recoil really means that carbine length systems should not be used where a mid-length system is practicable.

        Mid-length systems are not found in military weapons because they are intended for 16-inch barrels (although they can be used for barrels of 14 to 20 inches). The distance from the port to the receiver is 9 inches. Mid-length systems have softer recoil and are not as hard on the weapon, and, for that reason, are preferable to the carbine length gas system where practicable.

       Rifle length systems are intended for the 20 inch or longer barrels, although you will sometimes see it on 18 inch barreled systems.

Muzzle Devices

       Muzzle devices, other than silencers, fall into three categories: flash hiders (which purpose is to prevent the shooter from being blinded by the muzzle flash), muzzle brakes (which are designed to reduce or eliminate recoil), and compensators (which are designed to reduce muzzle climb due to recoil). However, many muzzle devices on the market combine two or more of these categories. For instance, it is common to see a combination flash hider and compensator.

       The most common muzzle device on AR rifles and carbines is the A2 flash hider. The A2 does a good job of reducing the considerable muzzle flash from 5.56 mm ammunition; and, because there are no ports on the bottom of the flash hider (to keep from kicking up dust when prone), it also acts as a recoil compensator. There is certainly nothing wrong with the A2 flash hider, and if that is all you have, it should work well for you. However, if you would like to explore different options, The Truth About Guns also put together a comprehensive review of muzzle devices, which you can read here.

       For what its worth, my opinion is that for a combat rifle, a flash hider is more important than reducing the recoil--particularly from the 5.56 which already has light recoil. Most muzzle brakes redirect gas to the sides to mitigate recoil, which makes them loud to those to the sides of the firearm, or even the shooter. I would avoid muzzle brakes. If you want recoil mitigation, look at a combination flash hider/recoil compensator.

Winter Trigger Guards

       The mil-spec trigger guard uses a straight bar on the bottom that can be released on one end to open up the trigger guard for use with gloves or mittens. A lot of shooters and manufacturers choose to replace this straight piece with a fixed piece that is curved to provide a larger opening. Some manufacturers even produce lower receivers with the larger, curved trigger guard machined into the receiver body.

       I'm of two minds on this. While I like the curved trigger guard to facilitate a gloved finger in cool weather, it also leaves the trigger guard more open to a branch or piece of gear getting inside the guard. Also, if you are in extremely cold weather where you need to use mittens or an extra thick glove, even the enlarged trigger guards may not be large enough.

       I guess my point here is to not just reflexively replace the standard mil-spec trigger guard.

Charging Handle

       The mil-spec charging handle works, but that is about all that can be said about it. It is small and slick. After market charging handles can offer distinct advantages over the mil-spec charging handle, particularly in three respects: you can get a textured handle to prevent your fingers slipping off the handle, you can get extended handles to make it easier to get a good grip on the handle (something particularly important if you mount a scope on the rifle), and you can find handles that are ambidextrous, which is great if you are a lefty or need to charge the rifle with your right hand. Unfortunately, ambidextrous charging handles are expensive--generally at least $80 to $90 dollars for a good brand. But for good weapons manipulation, it may be worth it. On that note, I've used the Raptor ambidextrous charging handle, and have really liked it.

Ambidextrous Controls

       The mil-spec AR has its controls--safety/selector, bolt release, and magazine release, set up for a right-hand shooter. The safety/selector lever is only on the left hand side of the weapon (so it can be manipulated with the shooter's thumb), the bolt release is on the left side as well (so it can be manipulated by the shooter's off hand), and the magazine release is on the right side (so it can be pressed in using the shooter's forefinger). Obviously, if you are right handed, this will probably work for you. However, to make the weapon usable by left-handers, or to make some weapon manipulations easier, people like to try and add ambidextrous controls.

       The easiest and most common change is to add an ambidextrous safety/selector. Since the selector pin actually extends through both sides of the receiver, no modification to the receiver is needed. Simply remove the old selector, insert the new selector pin, and then attach the levers to both ends.

       Another change to the safety/selector is that various manufacturers offer "short-throw" selectors. The standard selector requires the selector lever be moved through a 90 degree arc to switch between safety and fire. However, by reshaping the selector pin, it is possible to have shorter throws, with 60 and 45 degrees being popular. I'm not convinced that the shorter throw holds an advantage for most shooters, but it probably doesn't hurt, either.

      Competitive shooters like to have the option to operate the bolt release with their shooting hand. There are a couple basic replacement parts for this. One, which does not require any modification to the receiver, is Magpul's BAD (battery assist device) lever or similar devices from other manufacturers. These run a lever from the bolt release down and through the trigger guard so it can be actuated by the shooter's forefinger. However, I've heard of complaints with these devices breaking or getting caught up. Certainly, they crowd up the trigger guard area, which is undesirable. Thus, whatever their benefit for competition shooting, I don't believe they have a place on a survival rifle.

      Another option is to install a device such as Aeroprecision's PDQ ambidextrous bolt release, although this will require cutting a small slot into the lower receiver.

      Another modification is the ambidextrous magazine release, such as this product from Norgon or a similar product from Arms Unlimited.

      I will note that although I've replaced the standard mil-spec bolt release with a slightly larger lever, I have not used ambidextrous magazine releases or bolt releases, so I don't have any personal experience to share with these products. But I could see these as being a definite advantage for the left-handed shooter.

Buffers

       One of the methods used in the AR system to manage the speed of the BCG for reliable running is the buffer. There are four standard weights of buffers:
  • The rifle buffer (used only with a rifle buffer tube and rifle stock) weighing 5.2 ounces.
  • The standard carbine buffer (for use with a carbine length system in a carbine length buffer tube) weighting 3 ounces. 
  • The H or H1 buffer for carbine tubes weighing in a 3.8 ounces.
  • The H2 buffer for carbine tubes weighing 4.7 ounces.
  • The H3 buffer for carbine tubes weighting 5.6 ounces.
The heavier buffers are intended for different length gas systems. For instance, the Canadian military uses an AR rifle that has a 20-inch barrel, with a rifle length gas system, but a carbine buffer spring and tube. They use the H2 buffer.

       This will probably be considered additional heresy on my part, but if your rifle can be tuned using a different weight buffer rather than installing an adjustable gas block, so much the better. Adjustable gas blocks add yet another mechanical system that could fail, are more expensive than a buffer, and may require the removal of the handguard in order to reach the adjustment screws.

Notes:

* Although there are sources that indicate that this report was from the late 1950's or even the early 1960's, the face of the report indicates that it was published in 1952.

** While the Army would greatly reduce their marksmanship standards as a result of Marshall's work, the Marine Corps generally continued to emphasize individual marksmanship.


Selected Sources and Additional Reading:

".223 Remington," Terminal Ballistics Research.

"4150 Carbon Steel vs 416-R Stainless – Which is Right for Me?" Faxon Firearms.

Adelmann, Steve, "AR Gas-System Lengths Explained," Shooting Illustrated (Sept. 2014).

Adelmann, Steve, "The Pros and Cons of Nitride Barrel Finishes," Shooting Illustrated (Dec. 2017).

Anderson, Wayne, "AR15 Barrels: Profiles, Fluting, and Dimpling," AT3 Tactical.

"AR-15 Bolt Carrier Groups – Features, Coatings, & Recommendations," AT3 Tactical.

"Barrel Length Studies in 5.56mm NATO Weapons," Small Arms Defense Journal (Feb. 8, 2012).

"Barrel Length vs. Velocity," Guns & Ammo (Oct. 2017).

"Carbine, Mid, or Rifle? A Beginner’s Guide to AR15 Gas Systems," AT3 Tactical.

Dean, Glenn and David LaFontaine, "Small Caliber Lethality: 5.56mm
Performance in Close Quarters Battle" (PDF), WSTIAC Quarterly, Vol. 8, No. 1 (Jan. 2008).

"Hard Steel: The AR15 Barrel Buyer’s Guide… Turbo edition," The New Rifleman.

"How Barrel Twist Rate Affects Ammunition Choice," Stag Arms.

Jeremy S., "The AR-15 Drop-In Trigger Roundup," The Truth About Guns (April 14, 2016).

Jeremy S., "AR-15 Muzzle Brake Shootout #3," The Truth About Guns (Oct. 25, 2016).

Lamb, Kyle E., Green Eyes & Black Rifles: Warriors Guide to the Combat Carbine (3rd Ed. Rev., 2008).

"M16A4 Assault Rifle," Military-Today.com.

McHale, Tom, "AR 15 Rifle – A Brief History & Historical Time Line," Ammo Land (April 15, 2016).

Morgan, Martin K.A., "U.S. M16: A Half-Century of America’s Combat Rifle," American Rifleman (Sept. 2017).

Mullin, Timothy J., Testing the War Weapons: Rifles and Light Machine Guns from Around the World (Paladin Press 1997).

Pannone, Mike, "The Big M4 Myth: ‘Fouling caused by the direct impingement gas system makes the M4/M4A1 Carbine unreliable.’" Defense Review (March 19, 2010).

Plaster, John, "Testing The Army’s M855A1 Standard Ball Cartridge," American Rifleman (May 2014).

"Reduced effectiveness of the 5.56 NATO due to shorter barrels" (PDF), CBJ Tech.

Rose, Alexander, American Rifle: A Biography (Delacorte Press: 2008).

Sweeney, Patrick, "Guide to Gunmetal," Rifle Shooter (Dec. 2011).

"Terminal Ballistic Performance of the 5.56mm Cartridge" (PDF) Tactical Briefs (Volume 2, Number 6 (June 1999)).

"The Data Driven AR15: Or Why the Best AR15’s are Data Driven," The New Rifleman (Feb. 14, 2017).

Trevithick, Joseph. "Gunmakers Have Sold AR-15s to Civilians for More Than 50 Years," Motherboard (June 16, 2016).

"What Type of Barrel Should I Choose?" Ballistic Advantage (July 19, 2016).

"Why are Colt 14.5 Socom Barrels So Accurate?" The New Rifleman (Dec. 1, 2017).

Zediker, Glen, "Buffer Stuff: Keep The AR Cycling Happily," Guns Magazine (July 2012).

Updated (4/16/2018): corrected a couple of typos.

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