Twist Rate

(Source)

      Doing some research recently, I stumbled across an article from Outdoor Life discussing why the .243 Winchester became an American classic, but the .244 Remington (introduced about the same time and offering virtually the same capabilities) fell into obscurity. The "myth" is that it had to do the rifling twist rate. Winchester introduced its rifle with a 1:10 twist that could stabilize both lighter bullets for varmint hunting (at the time, only 80 grain), but also heavier 100 grain bullets suitable for taking deer. Remington, on the other hand, introduced their rifle with a 1:12 twist that was well suited for the varmint round, but incapable of stabilizing the heavier 100 grain bullets. Thus, according to the "myth" the .244 never became popular because it had a reputation for poor accuracy due to it not working well with the longer, heavier bullets.

       The author of the article had always disputed the "myth." He thought that the reason was the different in quality of the rifles in which the calibers were introduced. Winchester introduced the .243 as part of its Model 70 lineup, while Remington introduced the .244 in its M-722, which was a much cheaper made rifle. However, the persistence of the "myth" decided the author upon conducting a test to see if such slight changes in twist and bullet length could really be the explanation.

       To minimize the variables, he used three Remington 700 actions, each using the same HS Precision stock, with barrels identical except for the twist rates, which were 1:12, 1:10, and 1:8, respectively. He then used 16 different loads and bullet weights, each being shot through all three barrels. The author discussed the results:

          Since the 1-in-12-inch-twist myth was the main object of the experiment, that was the barrel tested first. Beginning with Winchester's Supreme 55-grain Ballistic Silvertip load, groups were uniformly small, ranging from ½ inch to ¾ inch and always well under an inch. ... Moving on up to heavier bullets, accuracy was initially encouraging, with handloaded 100-grain Sierra Spitzers grouping slightly under an inch. ... 

        But a few good groups do not a comprehensive test make, and they can easily lead to false conclusions. ... As more and more of these loads were tested, it became increasingly clear that my theory was falling apart. To put it bluntly, the accuracy of some of the heavier bullets in the 1-in-12-inch barrel was awful. True, some of the bullets were not expected to do well in the slow twist, such as the Berger 105-grain or Sierra 107-grain VLDs (Very Low Drag), which shot all over the target as predicted. Because of its length and shape, this type of bullet requires an extra-fast spin to stabilize, and groups were as big as 10 inches in the 1-in-12-inch barrel. The bullet holes were the "keyhole" shape of unstable bullets not flying point-forward. But more of a puzzle was the fact that the Hornady 87-grain hollowpoint grouped beautifully, while a bullet weighing only three grains more (the 90-grain Swift Scirocco) keyholed all over the targets. Obviously, bullet shape and construction, and not just weight, were determining factors. 

        With the 1-in-10-inch-twist barrel, accuracy improved across the board, and I happily conceded that I had been all wet with my long-held notion about Remington's .244-caliber rifles. Furthermore, the 1-in-10-inch barrel delivered accuracy with bullets as light as 55 grains that was almost as good as that with the 1-in-12-inch barrel, which clearly indicated its all-purpose advantage over the slower twist. 

       But there was still more to be discovered about the peculiarities of rifling twist. For instance, of the two VLD bullets that performed so miserably in the 1-in-12-inch barrel, the 105-grain Berger now grouped beautifully in the ½-inch range while the 107-grain Sierra lobbed 6-inch groups and made elliptical holes in the target. Why would two almost identically shaped bullets, both well-made and differing in weight by a scant two grains, perform so differently? 

       This riddle was solved when we switched to the 1-in-8-inch barrel and repeated the test series. The Sierra VLD now grouped beautifully, but the Berger VLD grouped even better! One of the groups shot with Berger bullets measured exactly .250 inches-the best of the entire test series. Which goes to show that a 2-inch change in the rifling rate can transform scattered shots into bug-hole-size groups. 

       This exceptional accuracy with the 1-in-8-inch barrel was isolated to only a few loads, however, as groups tended to open up with other loads and bullet weights, demonstrating once again that extra spin can be too much of a good thing. There were no signs of bullet yawing (tilting) with the 1-in-8-inch barrel, but the characteristic sign of accuracy decay was two or three shots in a close central group with the other shots going wide by an inch or two.

In fact, when speaking of the .243, "Hornady, Barnes, Berger, Nosler, Cutting Edge, etc. recommend twist rates for their extra-long, non-traditional bullets. Hornady, for example, recommends a 1:8 or faster twist barrel for its .243 108-gr. ELD Match bullet. Berger recommends the same 1:8 for its 82-gr. .224 Match BT Target bullet and many others." Most off-the-rack .243s now have a twist rate of just a tad slower than 1:9.

       We see this variance in other rifles. For instance, the latter article notes:

5.56x45mm NATO/223 Remington was originally designed around a 55-grain bullet and 1:14 twist. To improve downrange performance they went to a 62-grain bullet and 1:9 twist. The U.S. military uses some 77-grain bullets, too, and they generally require a 1:7 twist. In any caliber, the longer the bullet, the faster the rifling twist needed to stabilize it.

Similarly, the 1:10 twist originally developed for the .30-06 (back when it was the .30-03) was for a short, stubby round nosed 220 grain bullet. That same twist rate worked great for 172 grain and 150 grain bullets later adopted by the military, but a modern 220 grain boat tail bullet would probably not stabilize on the 1:10 twist. I had a similar issue with .308--147 grain bullets that grouped wonderfully out of one rifle, were all over the paper using a different rifle built for the larger hunting rounds. However, when I bumped up to 168 grains, the second rifle gave wonderful accuracy.

       Just something to keep in mind. If you get a rifle that seems to be a lemon, first try some different weights/loadings of ammunition in it.