
Originally Posted by
MistWolf
Bullet length and shape is more important to determining what RPM is needed to stabilize the bullet in flight than it's weight. The TSX is a solid copper bullet and is longer than a lead core bullet of the same weight.
Sierra uses doppler radar to measure the ballistic coefficient of bullets in flight. They have found the more stable the bullet, the less drag it has because it has less precession. The Sierra 69 gr Matchking (which is shorter than the 70 gr TSX), was found to have a better BC when fired from a 1:7 twist barrel than anything slower, including the 1:8.
The biggest problem with faster RPMs is that it's hard on lightly constructed bullets. In the late 60s, my father bought a 22-250 and developed a firewalled load using the Hornady 50 gr bullet, one designed to give explosive terminal performance on small critters at 223 velocities, that pushed it close to 4000 fps. We called it the Blue Streak Express because whenever he fired it, the bullet would leave a faint trail of blue smoke behind it. Turns out Dad was driving that bullet to the point it was on the verge of self destructing from the centrifugal forces. Twist on that rifle was 1:12.
Today's 22 caliber bullets are made to withstand being shot from the ever popular 22-250 and there is little danger of them coming apart when fired at the reduced velocities of the 223/5.56 even with their tighter twist.
There are more and more reports from serious shooters showing a trend that the 1:7 twist does indeed have an edge accuracy over the 1:8 at longer ranges
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