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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Barrel twist rate's affect on pressure
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<blockquote data-quote="Kevin Thomas" data-source="post: 482289" data-attributes="member: 15748"><p>Airstream,</p><p> </p><p>A little something to ponder here. Military ammo is loaded <u>hot</u>, usually right up to the max pressures allowable. The original M16 rifles had 1x14" twists for use with the 55 grain FMJ M193 (3,250 fps from a 20" barrel). This twist was increased in the M16A1 rifles to 1x12", with no problems at all in the ammunition/pressure department. They've now gone to a 1x7" for our M16A2s, A4s and M4 platforms. They still produce and issue the M193 ball ammo for training purposes, again with no problems at all. Doubled the twist from 1x14" to 1x7" and it doesn't create a problem. No, that 1" difference won't mean a thing to you in terms of pressure.</p><p> </p><p>The other question I'd have here would be is the barrel buttoned or cut? Cut barrels are usually closer to their advertised twist rates, where buttoned barrels can vary quite a bit. Some makers are better about this than others, but I've seen them vary by well over +/- a half inch (one inch total) from their stated twist. With the 140-142 grain bullets, that's a bit too close to the edge, in my book.</p></blockquote><p></p>
[QUOTE="Kevin Thomas, post: 482289, member: 15748"] Airstream, A little something to ponder here. Military ammo is loaded [U]hot[/U], usually right up to the max pressures allowable. The original M16 rifles had 1x14" twists for use with the 55 grain FMJ M193 (3,250 fps from a 20" barrel). This twist was increased in the M16A1 rifles to 1x12", with no problems at all in the ammunition/pressure department. They've now gone to a 1x7" for our M16A2s, A4s and M4 platforms. They still produce and issue the M193 ball ammo for training purposes, again with no problems at all. Doubled the twist from 1x14" to 1x7" and it doesn't create a problem. No, that 1" difference won't mean a thing to you in terms of pressure. The other question I'd have here would be is the barrel buttoned or cut? Cut barrels are usually closer to their advertised twist rates, where buttoned barrels can vary quite a bit. Some makers are better about this than others, but I've seen them vary by well over +/- a half inch (one inch total) from their stated twist. With the 140-142 grain bullets, that's a bit too close to the edge, in my book. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
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Barrel twist rate's affect on pressure
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