I previously mentioned that when the military switched to 62gr M855 5.56 ammunition that necessitated the switch to a 1/7 twist barrel. I am going to elaborate on the story before and after that event. In the 1950s when the AR-15 was designed, it was first made for .222 Remington, a story for another time. After they switched to .223 the rifling twist was 1/14. This denotation means that the projectile spins one full revolution in every 14 inches of flight. This was sufficient to stabilize the 55gr bullet they were using and the 54 grain M196 tracer bullet. However with the everlasting controversy of the adoption of the AR-15 this was brought into question. In arctic conditions where the barometric pressure was higher and the temperature was lower, the 1/14 twist was not sufficient to stabilize the M196 tracer. This became the focal point of an attack on the accuracy of the AR-15 in testing. Which you may think is retarded, but that is just one example of many in the history of people acting retarded in relation to the AR-15. Anyways, after this deficiency was harped on, the rifling twist was switched to a 1/12. The very early rifles sent to Vietnam (Colt 601s and 602s) used this early 1/14 rate. And these rifles were the ones notorious for creating immense wounds in enemy combatants. The rounds were on the verge of stability and would more quickly yaw and tumble in flesh. The 1/12 twist rate produced greater stability and the projectile would not tumble as quickly on impact. All AR-15 rifles produced from the 1963 to 1983 time period used this 1/12 twist rate. And again, after NATO selected the 62gr M855 ball cartridge and its accompanying M856 tracer, the 1/7 twist became necessary to stabilize it. Firing 62 gr ammo out of a 1/12 barrel will cause tumbling in flight in less than 25 yards. You will produce groups of about 200 MOA. This marks the end of the story of twist rate in reference to the U.S. military, the 1/7 is still standard and has been for 40 years. But in the civilian market the story is far from over. Colt adopted the 1/7 on their civilian rifles at the same time as on their contract rifles. But other makers such as Bushmaster adopted other twist rates. 1/9 and later 1/8 became popular twist rates in civilian rifles. The general consensus is that 1/7 doesn’t produce good accuracy in comparison to 1/8 or even 1/9. 62gr projectiles can be stabilized out of any of these twist rates, only the longer tracer M856 mandated the use of 1/7. So on many civilian market guns today you will find 1/8, and 1/9. 1/9 is seen as a more antiquated twist rate as it cannot cope with the higher grain ammunition popular with long range shooters, like 77 or 80 grain. Older Bushmaster rifles and some available from companies like Smith & Wesson use this twist. More premium manufacturers like Criterion generally stick to 1/8, giving you superior accuracy to 1/7 but the ability to use the widest range of ammunition. | Now, there are outliers. Twist rates like 1/6.5 or 1/7.7 are out there, available from manufacturers who think they know a lot more than they do. And the 1/14 twist has made a comeback, specifically used by varminters who use bullets with a MAXIMUM weight of 55 grains, more often, 50 or even 40 grains. They push them out there with insane speeds and nearly split coyote in half with them. 1/12 can also be found commercially on barrels meant to be used in retro styled rifles, typically 20 inch pencil barrels for M16A1s and 14.5 inch barrels for 653s and 654 carbines. For my mileage twist rate should be one of the last things on your list to worry about. I would deem that for a general use rifle even a 1/14 barrel would be totally fine, because shooting anything other than 55gr ball is typically only done as a “gee whiz” to see how tight your barrel can group with some 69gr $2.40 a round match ammo. For a purebred marksman rifle a 1/8 or 1/7 are both sufficient, but 1/8 probably more desirable. Twist rate is moreso useful as an indicator of the quality of the barrel or purpose of the barrel at a glance. Something in 1/7 is probably chasing the “mil-spec” title, and should be looked at with that lens. Something in 1/8 is trying to be a more precision oriented rifle. 1/9 means it was made circa 2004. Just know that it doesn’t matter as much as some people think it does. I like 1/12. But I cant buy good barrels in 1/12 because nobody else wants them. My custom dream AR would be in 1/14 and blow softball sized holes out of people. Your mileage may vary. Tune in next time when I tell you how .223 Wylde is a meaningless term. |
