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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Ordering new LRR build last minute advice!
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<blockquote data-quote="Bart B" data-source="post: 802269" data-attributes="member: 5302"><p>The rifling twist rate may change muzzle velocity 5 fps going from a 1:12 to 1:11. The amount's not an issue and extremly hard to measure accurately. In several decades of shooting high power rifle matches, I never heard any of the top scoring folks worry about twist rate effecting muzzle velocity; the best one will pick a barrel that's 5% more accurate over one that shoots bullets 5% faster. Nor am I aware of anyone conducting tests with two barrels having absolutely equal chamber, bore and groove dimensions shooting the same ammo and the only difference being twist rate that's published anywhere. I think folks claiming measurable differences are WAGing their numbers. WAGing = wild *** guessing; not scientific at all. Go calculate the rifling angle differences and see how tiny they are. There's a greater spread in muzzle velocity for a given load for the life of the barrel than a small difference in rifling angles has.</p><p></p><p>More important is that one should not spin bullets any faster than needed to stabilize them all the way to the target. Too fast and the bullet's tiny unbalance issues will cause too much of a jump off the muzzle axis as they exit. A 1:10's ok in a .308 for 200 and 220 grain bullets, but a bit fast for best accuracy with lighter ones. If your heaviest bullet will be at 180 grains, then a 1:12 twist is ideal for them and others down to 150 grains; a 1:11 if you'll be shooting in cold weather below 40 degrees F.</p></blockquote><p></p>
[QUOTE="Bart B, post: 802269, member: 5302"] The rifling twist rate may change muzzle velocity 5 fps going from a 1:12 to 1:11. The amount's not an issue and extremly hard to measure accurately. In several decades of shooting high power rifle matches, I never heard any of the top scoring folks worry about twist rate effecting muzzle velocity; the best one will pick a barrel that's 5% more accurate over one that shoots bullets 5% faster. Nor am I aware of anyone conducting tests with two barrels having absolutely equal chamber, bore and groove dimensions shooting the same ammo and the only difference being twist rate that's published anywhere. I think folks claiming measurable differences are WAGing their numbers. WAGing = wild *** guessing; not scientific at all. Go calculate the rifling angle differences and see how tiny they are. There's a greater spread in muzzle velocity for a given load for the life of the barrel than a small difference in rifling angles has. More important is that one should not spin bullets any faster than needed to stabilize them all the way to the target. Too fast and the bullet's tiny unbalance issues will cause too much of a jump off the muzzle axis as they exit. A 1:10's ok in a .308 for 200 and 220 grain bullets, but a bit fast for best accuracy with lighter ones. If your heaviest bullet will be at 180 grains, then a 1:12 twist is ideal for them and others down to 150 grains; a 1:11 if you'll be shooting in cold weather below 40 degrees F. [/QUOTE]
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Ordering new LRR build last minute advice!
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