View Full Version : Barrel twist for 223 55gr Barnes Triple Shock
12-18-2011, 10:32 AM
I want to mount mount a scope on one of my AR's to use for deer hunting and can choose between two rifles, one has 1:7 twist and the other has 1:9. Both have 16" barrels chambered for 5.56 NATO. The ammunition is by Federal in 223 cal using the Barnes 55 gr Triple Shock (TSX) bullet.
Barnes website says 1:9 or faster so either should work but if anyone has tried both twists with this bullet I'd appreciate your feedback.
12-18-2011, 10:37 AM
Copied from Diesel
12-18-2011, 10:48 AM
I've seen that chart but these all all copper bullets that are longer than the same weight lead bullets. It's the length of the bullet that matters, not the weight.
I'm hoping someone here has used this ammo and can share their experience.
12-18-2011, 11:28 AM
It is largely a myth that there is such a thing as too much barrel twist for proper stability. If you look at the physics and the resulting equations you do not see any factor that would indicate such a thing as too much stability.
There is one possible exception to this reasoning. If the bullet you are using is not balanced (the center of gravity about the rotational axis is not in the same place as the center of rotation), then the bullet will exit the barrel at a small angle to the centerline of the barrel. The size of the angular offset is dependent on the amount of imbalance and the spin rate of the bullet. However, if you plug in the numbers you will find that for anything other than some horrifically badly balance bullet (or for guns that would otherwise shoot 0.05 MOA) the error is insignificant. I once calculated that the amount of error in accuracy one is likely to get from an average imbalance bullet from a .308, amounts to 0.1MOA. Solid bullets typically have the smallest possible imbalance (due to a homogeneous structure) so they would have substantially less imbalance related error than 0.1MOA. But also keep in mind that this imbalance error is always present regardless of barrel twist or bullet length, it just becomes larger with faster twists. Going from a 1:9 to a 1:7 might change this error from 0.02 to 0.03MOA but either way it would be insignificant to anyone but a world class benchrest shooter. Benchrest guys do tend to use the least twist required to stabilize the particular bullet they are using, but their reasoning does not make sense to anyone shooting even a sub MOA AR-15. Our accuracy level is simply not good enough for the imbalance error to be meaningful with anything short of a purposely imbalance bullet.
One final exception to this reasoning. If you shoot very very light bullets with very fragile jackets it is possible to spin the bullet fast enough to tear off the jacket. I have not personally ever seen this happen but I have seen videos that seemed convincing. There is no danger to the shooter but the bullet essentially tears itself apart when leaving the barrel, and downrange you have something more akin to a shotgun blast than a bullet hole. I have shot bullets as light as 30 grain from a 1:8 barrel and did not see any issues with accuracy or jacket sheading.
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