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Posted: 9/21/2002 12:46:31 AM EDT
| Could someone please advise which twist rate will produce the most accurate of shots. I know that the military uses a 1x7 to suit the wide varity of rounds they use. If all you intend to shoot is a 55gr 5.56 would a 1x9 be the way to go? Does 1x9 stablize a 62 grain round? Thanks |
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leo6223 The 1x9 seems to be the best all around twist rate. It should be able to stabilize any where between a 40 - 75 grain round. If you would like more information about 5.56 ammo and twist rates go to www.ammo-oracle.com -JoeyD |
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So here's the real question: Although it seems like 1x9 is the BEST for 55grain, will I be sacrificing much if ANY accuracy with the 1x7? Here is the dilemma... the rifle is a "spotters" rifle so obviously accuracy is essential but so is fragmentation (instant incapacitation is a must). Paper targets are one thing, humans are another. There seems to be so many trade offs: Accuracy-fragmentation-time to stabilization (most LE shots are under 70yards...so this is key). If you had to pick under this scenario what would be your choice? Perhaps a easy way out...the 1x8? |
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In 1980, NATO approved the adoption of the 5.56 x 45 mm NATO cartridge as the second standard caliber, and the Belgian SS109 as the basis for standardization of ammunition. The SS109 bullet design utilizes a 62 grain Full Metal Jacket Boat Tail (FMJBT) projectile. To achieve proper spin stabilization of that long, heavy bullet, a fast twist rate was required. Barrels with a 1:12” riffling twist offer best accuracy with bullet weights from 45 to 55 grains. Although bullets from 40 to 60 grains can be stabilized, accuracy will not be optimum. The common 1:9” twist remains optimum for bullets weighing between 55 to 70 grains. Although lighter bullets can be used in a 1:9” barrel such light weight bullets may be over stabilized and accuracy may suffer. A 1:7” barrel will offer best accuracy with heavier, longer bullets from 68 to 80 grains. Accuracy with these fast twist barrels with lighter bullets is poor. As noted there is an over lap between the various barrel twists. With typical military surplus and factory ammunition being between 52 and 62 grains the common 1:9” barrel has the most utility. Those wishing to compete in long range target shooting where the heavy 70 grain bullets are hand loaded to lengths that won’t fit in a standard magazine the faster 1:7” twist rate will stabilize those bullets for the most accuracy. ... from my web site. |
I'm 'guessing' that you're probably going to want a CQB M4 type weapon for the scenario above. If so, I would get a 1:7 barrel and shoot the heavier bullet. You'll get better knock-downs and also so some ability to penetrate light barriers that a perp might choose for concealment. Much better than what I would do is that the military in the Afghan did what I propose to you. Far, FAR too many short barreled, low velocity weapons employed there and finally the military changed to a heavier bullet for the reasons described above. |
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