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Posted: 10/3/2014 10:03:34 PM EDT
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I want to build a .204 Ruger upper. There are a couple different barrel twist options out there - typically 1 in 12 and 1 in 9 inch. I know the heavier bullets require a faster twist to stabilize them but I don't really plan to use those.
However, I wondered if there's any sort of penalty paid in velocity, accuracy, etc. to just go with the fast twist and shoot lighter (ie. 32 grain) bullets. Or go with 1 in 12 and know I can't shoot the heavies. Thoughts? |
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This tech note by Armalite is worth reading. It has a formula, the Greenhill Formula, that can be used to calculate roughly the twist rate to stabilize certain bullets by length and diameter since bullet weight is not a factor in determining twist rate.
Armalite Technical Note 110: Projectile Weight Versus Rifling Twist |
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Thanks for that article. It was perfect. And to those that answered that it makes no difference - it definitely does. (here's the quote from the article below). The 3rd would most important to me but they all are important tradeoffs - especially at around 4000 fps. Sounds like 1 in 12 for me.
"So, you ask, why don’t we just build all rifles with a twist fast enough to stabilize any projectile regardless of its length? We don’t because, as my Harley-riding friend, Dr. Demento, used to say, “There Aint No Free Rides”. There are always tradeoffs. In this case, there are three significant tradeoffs. --First, if you spin a projectile LOTS faster than is necessary to stabilize it, you actually overstabilize it, causing it to be somewhat less accurate than it could be with the proper twist. Certainly overstabilization is better than understabilization. But, for the very best in accuracy, the projectile should be adequately stabilized, not significantly overstabilized. --Second, spinning the projectile places great stress on the rifling. The faster the twist, the more the stress. So, barrels with faster twists tend to wear out more quickly than barrels with slower twists. --Third, some projectiles have relatively fragile jackets (notably varmint bullets). Spinning these projectiles too fast can cause the jackets to rupture in flight. |
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