Thursday, August 21, 2014

From the Archive: Building an AK

Below I've posted some thoughts and tips I picked up building an AK from a parts kit that I published in January and February 2012. It has been a fun gun to shoot.

* * * * Part 1 * * * *

With the successful resolution of my failure-to-extract issue, I've decided to discuss my thoughts (and lessons learned) on building an AK-74. This is not intended to be a primer (there are several sources of detailed information on builds available on the internet) but just a few pointers, ideas, and what I learned from the project.

Please note that I am not a gun smith, engineer, or machinist. These tips and thoughts are based on my own experience and are for educational use only. You should obtain proper instruction and training before attempting to use any tools or assembling a firearm. If you decide to use or apply these tips and thoughts, you do so at your own risk.

You Will Not Be Saving Any Money

First, and foremost, I want to emphasize that it is no longer economical to attempt to build an AK from a parts kits.Several years ago, you could get a de-milled AK kit (generally a Romanian AKM "G" kits) for around $70 dollars, that included the original barrel already seated in the front trunnion. Other types of kits, such as Polish underfolders, Egyptian made models, etc., were a little more, but included a barrel. The difficult part--seating the barrel and cutting the slots for the pins--was already done. This made it easier, and less expensive, for you--or a gunsmith if you sent the parts off for assembly--to build the rifle.

Then the Bureau of Alcohol, Tobacco, & Firearms (BATF) changed the import rules. The result is that kits are now much more expensive, and do not come with an original barrel (or have a demilled barrel, i.e., a barrel with a several large holes drilled into it rendering it useless and irreparable). When you add the expense of purchasing the barrel to the other 944r parts, it is nearly the same as buying a finished gun from someplace like Century Arms. When you add the costs of a gunsmith to assemble the parts (or the tools, if you are going to do the assembly yourself), you easily could be paying as much or more than you would for a really nice AK from K-VAR. My opinion is that if you are going to build an AK from a kit, it must be because of the joy or interest in the project, to test your skills or learn new skills, and not because you are trying to save a few bucks.

Parts

Obviously, the basic set of parts you will need will be a "parts kit"--generally this will include both the front and rear trunnions, gas tube, front and rear sight assembly, trigger group (the hammer, sear, and trigger unit--typically for select fire, unless from a Romanian "G" model), stock, pistol grip, top cover, recoil spring, bolt, bolt carrier and gas piston, and various springs and pins. Some sellers may include a U.S. made barrel as part of a packaged deal. If not, you will need to purchase a barrel separately.  Sometimes you can find an East Bloc barrel that is mil-spec with a chrome lined bore and barrel. Otherwise, you will need to get a U.S. barrel. To my knowledge, there are no U.S. made barrels that are chrome lined. Sources for barrels, parts kits, or individual parts, include ApexCenterfire SystemsCheaper-Than-DirtCopes DistributingSarco, and RTG Parts. There are plenty of other sources out there as well.

The next "part" is technically the firearm. This is the receiver. This is the part that is registered and bears the serial number. You have two options: (1) buy a fully manufactured receiver through a licensed firearms dealer, or (2) buy a receiver "flat" and manufacture your own receiver. The welding and bending of a "flat" is beyond my skills and ability, so I will not discuss it, but Tapco manufactures flats. There are several manufacturers of AK receivers, but I used one from Nodak Spud. If you have a gun dealer you work through, you can place an order with Nodak, then have the FFL holder fax his license to Nodak. The receiver will be shipped to the FFL holder, where you will complete the paper work for the transfer. Check about the transfer fee charged by the FFL before you order the receiver.

Next, you need to purchase parts to comply with BATF Regulation 944r. I won't go into it in detail, but essentially you need to have a certain number of key parts manufactured in the United States. Tapco has a good overview on their website (link here). Not all guns have the total number of parts in the list. My understanding is that you will need to get at least six (6) U.S. made parts for the AK, but I also recommend that you "overbuild" it with additional parts just to be safe.

The barrel and receiver are each one (1) part, so by this point, you already have two 922r parts.

You will also need to get a different trigger group since you can't use the select-fire/full auto trigger group that came with the kit. A new hammer, trigger and sear all count as a 922r part each, so a complete trigger group is three (3) additional parts. As you can see, just replacing the minimum parts you need already gives you 5 of the 6 required parts. I used an Arsenal Inc. made trigger group (available through Midway or K-VAR), but Tapco's trigger group has also received high marks.

A couple notes as to the trigger group, however. First, there are single-hook and double-hook triggers available. You can read up on the differences on the internet. However, the receiver has a small slot in front of hole for the trigger to accommodate the hook when the trigger is pulled. That means that a single-hook will need one-slot, but a double-hook will need two-slots. Not all receivers are built with two slots. So, unless you fancy yourself cutting a slot into the receiver, check your receiver before you order the trigger group. I used a single-hook so I didn't have to worry about the issue.

Second, you may be tempted to pitch the full-auto trigger group that came with your kit. Don't. There is a small spring that fits between the trigger and the sear that you will need. Take the trigger/sear/rate reducer apart after wrapping in a cloth. The spring will jump out, so the cloth will catch it. (Trust me, the spring is very small and hard to find). After you have removed the spring, then you can throw the old trigger parts away.

The other parts to replace with 922r parts depends on your taste and what you want. If you want to use a non-U.S. stock and/or pistol grip, you may have to get creative. However, the stock is the easiest part to replace. The fore-stock, pistol grip, and butt stock are each one part, so replacing all three would give you a total (with the receiver, barrel, and trigger group) of 8 parts, which is well in excess of what is required under 922r.

Another part that is easily replaced is the flash-hider/muzzle compensator. The gas piston can be replaced, and some people will use U.S. made magazines (three parts--body, floor plate, and follower) or use a U.S. made floor plate or follower on a foreign made magazine body.

I opted for a U.S. made stock set. I chose the set available through K-VAR because it was the only U.S. made synthetic stock set with a heat shield in the forestock. (Note: K-VAR also sells foreign made stock sets, so double-check what you are ordering).

Another part you may consider, although it is not necessary, is a retaining plate to hold the trigger group pin in place. Tapco builds one (link here).  Here is a different style (a "shepherd's crook") at Brownells. (Link here). You can also modify one of the springs to clip into place. Strangely enough, Tapco has modified spring clips that you can also get (link here). I've had experience with the shepherd's crook style, but made my own spring clip out of a spring. (Some instructions here). It will save you a lot of time and expletives if you use a retaining plate.

Once you have the parts you need, you can ship it off to a gunsmith to assemble. Otherwise, you are ready to start down the hard road of becoming a DIY gunsmith.

Rivets Versus Screws Versus Welding

For the DIY gunsmith, the next issue is deciding the method to assemble the component parts--specifically, attaching the receiver to the front and rear trunnions, as well as attaching the trigger guard and magazine release assembly to the receiver.

The great debate (and it can be contentious) is using rivets versus using screws. You will also find a few people discussing welding. As I noted above, I don't do welding, so I won't discuss that option any further. The people arguing for rivets make two basic arguments: rivets are what the original design called for; and screws are too weak and loose to hold the gun together. Well, there is no doubt about the use of rivets by the Soviets, but in my research, I never came across anyone that actually experienced a failure due to a screw breaking. If there were any problems with screws, it was with the screws backing out, which problem was solved with a bit of Lock-Tite.

I decided on a screw build. My reasoning was that I thought it would be easier than attempting to build with rivets, it would be cheaper, and if I had issues, I could dissemble the parts if I needed. One of the issues that particularly concerned me with a rivet build was the actual process of squeezing the rivets. The professionals that built lots of AKs had special jigs for use with a hydraulic  press, which cost several hundreds of dollars. Other people modified bolt cutters to use to squeeze the rivets.

However, whichever way you go, you will need to get either rivets or screws. Various companies make rivets for assembling an AK. Screw kits were harder to track down. Although Tapco makes a set of screws, you can't purchase directly from Tapco, and there were only a couple of parts dealers that carried the screw sets. Of course, you can also go to your local hardware store for the screws, which is what I did, selecting stainless steel screws. If you do go the screw build route, I would recommend getting two sets of the screws just in case.

Tools

I'm going to assume that anyone getting into a project like this has basic hand tools like a ball-peen hammer, punches, various types of pliers, a vice-grip, etc. I also assume that you have some lubricant for easing the barrel and various pins into place. My focus will be on some of the non-standard tools.

Since you will be seating (pushing) the barrel into the front trunnion, you will want a hydraulic shop press. (Here, for example). This will come in handy for pressing the barrel pin. I suppose that you could use a heavier hammer to hammer the barrel in place, but it is a whole lot easier to have the press.

You will have to cut slots in the barrel for various pins, and you may need to open up some of the holes in the receiver for the screws. For this, you will need a Dremel or similar rotary tool. For the actual cutting, you will want to get 1/8 inch tungsten carbide cutter (Craftsman parts no. 953071) and 5/16 inch diamond point cutter/engraver (Craftsman parts no. 953161). The latter actually comes with two cutters/engravers--you will only need the pointed one; the one with the bulb tip is unnecessary for this project.

Of course, if you decide on a screw build, you will need the appropriate sized and thread tap and a tap wrench.

I discovered that the hole in the front trunnion for the barrel was actually too small. Ideally, you would use a flapper wheel to open it up but keeping it uniform in diameter. However, I couldn't find one that was the right size. I eventually decided on a 1-1/8 inch brake cylinder hone. (See, for example). It was still too big, but by removing one of the stones, I was able to fit it in and broaden the hole. If you have to do this, be very careful--you want the hole to be big enough that you can fit the chamber end of the barrel into the front trunnion, but tight enough that you will have to use the press to seat the barrel. In my case, just a few seconds of use (probably enough to grind off 1/1000 inch of material) was enough.

In my next post on this topic, I will discuss tips and pointers as to the actual assembly process.

* * * * Part 2 * * * *

This is the second part of my post on building an AK74.

Please note that I am not a gun smith, engineer, or machinist. These tips and thoughts are based on my own experience and are for educational use only. You should obtain proper instruction and training before attempting to use any tools or assembling a firearm. If you decide to use or apply these tips and thoughts, you do so at your own risk.

Threading the Trunnions

To do the screw build, you will obviously have to thread the holes in the front and rear trunnions. Remember, use plenty of oil and go slow and easy, backing the tap out often and cleaning and oiling it. I wasn't so careful on the first hole, and ended up breaking off the tap (which was a major task to get out).

Remember that on the back most hole on the rear trunnion, you will actually be threading it to accept a screw from both ends. It's easier to tap from both sides rather than try to run the tap all of the way through.

Prepping the Receiver

Check to make sure that the rivet holes in the receiver are big enough for you to slide the screws through. You don't want the screws threads to catch on the sheet metal of the receiver; instead, you want the screws to pull the metal wall of the receiver tight against the trunnions. The metal for the Nodak receivers have been heat treated, and they will strip the threads off the screws if the holes are not big enough. A quick pass or two with the 1/8 inch cutter should be sufficient to open up the rivet holes.

Seating the Barrel

As I stated above, the hole in the front trunnion for the barrel was too small for my barrel (the barrel was slightly oversized), so I had to "hog out" the trunnion slightly, which I discussed above in the tool section.

Remember to use a coating of lubricant on the barrel as you seat it. If you are using a press, just take it slow. The load pops are disconcerting, but normal.

Preliminary Assembly

At this point, you will need to check the head space, so screw the front and rear trunnions into place. DO NOT use Lock-Tite yet--you may need to remove the front trunnion again.

Headspace

Before you cut the slot for the barrel pin, you need to make sure that the head space is correct. I won't get into detail on the importance of proper head space because there are plenty of articles in gun magazines and on the internet discussing the topic.

The issue we have is measuring head-space. Typically, you would want to check head-space using a "go" and a "no-go" gauge. These gauges mimic a rifle cartridge. The bolt should be able to close all the way on a "go" gauge, but not be able to fully close on the "no-go" gauge.

The problem I had is that there is apparently only one manufacturer of these gauges for 5.45x39 firearms, and the gauges each cost some $30 or $35 dollars, which seemed excessive since I was only going to be building one firearm.

I came across a work around on one of the gun boards. First, you have to fit both trunnions into the receiver, with the barrel pressed in to where you think it should be, and screw the trunnions into place. This should be enough to put the bolt and bolt carrier into place. The trigger assembly and hammer are not yet installed. You will need two cartridges. One, unmodified, will be your "go" gauge. The other will have 3 layers of transparent tape ("Scotch tape") placed over the base and trimmed around the edges. This is the "no go" gauge. I fitted these into place and closed the bolt on each, and they worked--the bolt would close on the "go" cartridge, but not close on the "no-go" cartridge.

I had seated the barrel at the correct depth so I didn't have to mess around with the barrel. However, this is the step where it is useful to have used screws, because you could simply remove the front trunnion/barrel assembly from the receiver if you had to adjust the head space.

Seating and Pinning

The next steps are fitting and pinning the rear site assembly, the gas port, and front site frame. As with the front trunnion, you made need to slightly enlarge the holes on gas port assembly and front sight to get them to fit over the barrel. Again, they should fit over the barrel, but not necessarily be easy to get on--they need to fit tight.

The 1/8 inch cutter can be used to cut the slot for larger barrel pin--just put the cutter into the pin hole and start cutting it out so that the "hole" goes all of the way through. Remember to go in from both sides, and clean out the metal. I used a standard round file to smooth things out. This will take time. I thought I had it "right," then found that the pin wouldn't go in all of the way, had to drive it out, and work some more on enlarging the slot. Sometimes getting the pin out was more challenging than the effort to get it in. It helped, on those cases, to have a block of wood with a hole bored into it. Just rest the weapon over the block so that the pin can be driven into the hole in the block, and use a hammer and punch to push the pin out. (I didn't find the press to be as useful for getting the barrel pin out as for seating it in the first instance).

The other pin slots will need the smaller diamond cutter. For a file, I used a chain saw file. Otherwise, it was the same process.

When using the file, be careful of getting them stuck. Don't twist or screw the file--always use a straight back and forth motion.

Locating the Gas Port Hole

The challenge with pushing the gas port down into position over the barrel is making sure that you have it positioned far enough back to securely hold the gas tube in place, but not so far back that the gas port hole is covered.

What I did is use a caliper and put one end over the gas port, and then put a small mark on the opposite side of the barrel with an indelible marker. There is a small hole on the bottom of gas port assembly (i.e., on the bottom side of the barrel) that I believe lines up with the opening for the gas inside the assembly. Anyway, that is the theory. I slid the gas port assembly down over the barrel until I could see the small hole. Then, using a piece of wire that I had fashioned into an L-shape, I felt around inside the assembly until I was able to push the wire through the gas port hole in the barrel. That is how I was able to check the position.

Then, checking and rechecking the fit of the gas tube and using the wire to gauge the position of the gas port hole, I tapped the assembly down until I had it in the proper position--i.e., where the gas tube was secure, but I was not covering the gas port hole.

Special Notes for the Sights

The problem you want to avoid with the sights is having them canted to one side or the other. I used a small level over the rear site assembly to get the main part of the rifle leveled, and then slid the front site assembly on the barrel with just my hand, but enough so that it would stay in place, and used the level until the sight was in place. During the process I would double-check the rear site assembly with the level to make sure I had not disturbed it. Since I had put the rear stock on prior to this, I also put it up to my shoulder just get a visual picture as well. When I thought that the front site assembly was level, I took it out of the cradle so that I could use the hammer and punch to press the front site assembly down over the barrel into its final position.

Trigger Guard

On a screw build, you will use small nuts inside the receiver to hold the screws into place. The back screw is no problem, but for the four (4) screws on the front of the trigger guard/magazine release, I found that I had to grind down the outside edge of the screw heads so they would fit, and also grind off one of the points on the nuts to get them to all fit together as well. Again, don't use Lock-Tite yet, because you may have to take the screws or nuts out to work on them.

Lock-Tite

At this point, I loosened up the screws a bit to apply some Lock-Tite and screwed them back down tight.

Finishing

My next step was applying a spray-on finish to the barrel, receiver, etc. This may take several days to cure, so patience. Make sure you have removed the rear stock if you had previously installed it before applying any finish.

Trigger and Hammer Assembly

Now its time to assemble the guts of the beast. You will first want to use a  soft metal (i.e., brass) cleaning brush with your Dremel to polish the trigger assembly parts--particularly where the parts will be rubbing together. Don't take off the coating, just polish it so its smooth.

I installed the pistol grip before installing the trigger assembly.

Not ever having assembled an AK trigger group before, this was an experience. It took a lot of work and patience to hold all of the parts in place against the force of the springs while sliding a pin into place. I used a small nail punch that I pushed in from one side to hold everything in alignment while I slid the pins in from the other side. (The hammer and trigger pins slide in from left to right; the "pin," rod, or whatever you want to call it for the safety lever is inserted from the right to the left).

I had two primary issues at this point. First, I didn't have enough clearance for the hammer and its spring, and it was binding against the nuts for the screws at the front of the trigger guard. I had to remove the hammer and spring, and grind a little off the top of the nuts.

Second, was fitting the spring-clip in to lock the trigger pin in place. As I noted earlier, just buy a retaining plate and don't bother with using a modified spring. Really. I modified the spring and used it just for the experience, but ....

Stock

The final step is to reattach the rear stock and install the front stock.

Results

The first time I took it out to shoot, I put approximately 100 rounds through it without any mechanical problems. If you have read my prior posts, you know that the next time out shooting, I had a failure to extract which occurred on the first round. After taking care of that issue, I went out again and put another 90 rounds through the rifle without any further issues.

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