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by Chad Haire .223 BARREL TWIST vs. ACCURACY Does the standard 55 gr. ammo perform well in fast 1-to-9 twist barrels? Our M-16 tells the story
Tucson, AZ- December 16, 1999 - For decades, the 5.56 mm NATO (.223) cartridge consisted of 55 gr. projectile fired out of barrels with a slow 1-in-12 inch twist. Lately, in attempt to gain more range , the trend has been to switch to heavier 62 gr. projectiles. To stabilize the heavier bullets, the rifles have been issued barrels with a quicker 1-in-9 or 1-in-7 inch twist. While the 1-in-12 inch barrel can’t stabilize the heavier 62 gr. bullet. We have been told the 1-in-9 inch tube will work quite well with either the newer 62 or older 55 gr. projectile. The most popular rifle to find out with is the AR-15/M-16 series. Several years ago, Colt discontinued their old style A1 rifles which had the 1-in-12 twist barrels, and created the A2 series with the faster 1-in-9 tube. Afterwards, the national gun publications kept telling us how accurate the new models were, even when firing the lighter 55 gr. cartridges. Problem is, this does not agree with numerous AR-15/M-16 shooters I have talked to, who claim accuracy with heavy .223 bullets, but lousy groups when shooting lighter projectiles out of their newer 1-in-9 barrels. THE TEST To find out what was true, and what was hype, I decided to conduct my own test. For the performance and accuracy evaluation, we purchase the following .223 ammunition.
For the best accuracy results, all shooting was conducted within military spec “sight in” guidelines. This involved placing a 250 meter simulator target 25 yards away. This procedure eliminates light distortion and windage problems, which were very present in the hot Arizona desert we were shooting in. The 5-shot groups (I consider that three shot groups are not precise enough) would be multiplied by 4 to get the equivalent 100 yard group, or minute of angle (MOA). TEST #1 First we fired AR-15 with 20-inch 1-in-12 inch barrel. Our PMC 55 gr. ball showed a 3.4 inch MOA. Second, the Winchester 55 gr. did 2.5 MOA. Third, IMI H.P. gave a 5-shot group reading 2.5 MOA. This is an average of 2.8 MOA overall. Next, we conducted the same firing sequence with our M-16 rifle. We got 4.5 MOA with PMC ball, which this particular rifle never liked anyway. Then 3.0 with Winchester SP, and 3.0 using IMI HP rounds. The overall reading was 3.5 MOA. Finally, the Colt Carbine with 1-in-9 barrel was fired. It showed 4.4 MOA with PMC ball, 4.0 for Winchester SP, and 5.0 with IMI HP. Overall average was 4.5 MOA. Time for some different ammo! TEST #2 Since the heavier 62 and 64 gr. bullets will not stabilize in 1-in-12 barrels, the only rifle used for this last test was the Colt A2 rifle with 1-in-9 tube. First, we shot the PMC 64 gr. soft-point ammunition. What a difference! The initial firing sequence gave us an MOA reading of 3 MOA, and next was a 2.5 MOA for 2.75 overall. Next, on out list was the Russian 62 gr. ball made by the JSC Barnaul Machine Tool Plant. This stuff came into the market just recently, and was selling for only $135 per thousand rounds as May 1999. Is it any good, you ask? Seeing how we obtained consistent 2-inch MOA groups, with some bullets going through the same hole on the target, I would say very much so! JCS also makes 55 gr. 5.56 mm ammo, but I could not find any for this test. CONCLUSION After I did this test, I discussed the results with many target shooters who use the AR-15 and M-16 system. he stories I heard were the same: Fast twist 1-in-9 and 1-in-7 barrels work fine with heavy bullets, but lose about 20-30% accuracy when using the standard 55 gr. projectiles, which were designed for slower 1-in-12 type. In spite of this many shooters use the lighter 55 gr. anyway because it’s much cheaper to buy , and more available. But if the 62 gr. JSC Russian ammo works as good in other rifles as did in mine, and continues to sell this cheap, this should no longer be an issue. In any case, those who are not getting acceptable accuracy from their A2 “fast twist” barrels have a clear choice: use heavier bullets or change the barrel.
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