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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
What twist to use?
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<blockquote data-quote="Bart B" data-source="post: 687582" data-attributes="member: 5302"><p>When those 22" barreled M14NM's and M1A's were popular for service rifles in competition their 1"12 twist barrels did great with bullet weights from 168 through 180 grains. Some folks used 1:11 twist barrels for those bullet weights but accuracy equaled what the 1:12 ones produced. I suppose if the weather and powder temperature was pretty cold, the lower muzzle velocity produced in a 22 inch barrel would be better for accuracy with the 1:11 twist.</p><p></p><p>The above aside, none of the above equalled the accuracy produced with 7.62 NATO chambered Garands using Sierra 190's in their 1:12 twist 24 inch barrels. </p><p></p><p>A 20 inch barrel's going to get lower muzzle velocities with the same peak pressure compared to a 22 inch one with the same load, chamber, bore and groove dimensions. So, as mentioned by others, a 1:11 will do well. Except for 168's past 700 to 800 yards; if they're Sierra's, they probably will slow down to subsonic speeds at that point and change direction a bit.</p><p></p><p>The US Army's Advanced Marksmanship Unit Team set a service rifle team record at this year's Nationals using AR10's with 20 inch barrels shooting Berger 185's:</p><p></p><p><a href="http://bulletin.accurateshooter.com/2012/07/usamu-teams-set-1k-records-at-interservice-championships/" target="_blank">http://bulletin.accurateshooter.com/2012/07/usamu-teams-set-1k-records-at-interservice-championships/</a></p><p></p><p>I've no idea what load was used, but the military rifle teams have a long history of using handloads close to blue pill (proof load) pressures.</p></blockquote><p></p>
[QUOTE="Bart B, post: 687582, member: 5302"] When those 22" barreled M14NM's and M1A's were popular for service rifles in competition their 1"12 twist barrels did great with bullet weights from 168 through 180 grains. Some folks used 1:11 twist barrels for those bullet weights but accuracy equaled what the 1:12 ones produced. I suppose if the weather and powder temperature was pretty cold, the lower muzzle velocity produced in a 22 inch barrel would be better for accuracy with the 1:11 twist. The above aside, none of the above equalled the accuracy produced with 7.62 NATO chambered Garands using Sierra 190's in their 1:12 twist 24 inch barrels. A 20 inch barrel's going to get lower muzzle velocities with the same peak pressure compared to a 22 inch one with the same load, chamber, bore and groove dimensions. So, as mentioned by others, a 1:11 will do well. Except for 168's past 700 to 800 yards; if they're Sierra's, they probably will slow down to subsonic speeds at that point and change direction a bit. The US Army's Advanced Marksmanship Unit Team set a service rifle team record at this year's Nationals using AR10's with 20 inch barrels shooting Berger 185's: [url]http://bulletin.accurateshooter.com/2012/07/usamu-teams-set-1k-records-at-interservice-championships/[/url] I've no idea what load was used, but the military rifle teams have a long history of using handloads close to blue pill (proof load) pressures. [/QUOTE]
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