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Rifles, Reloading, Optics, Equipment
Reloading
Crimp or no crimp for semi automatic rifless
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<blockquote data-quote="Bart B" data-source="post: 1131612" data-attributes="member: 5302"><p>For what it's worth, people winning the big matches and setting records in NRA and CMP matches shooting AR platforms using the .223/5.56 round never ever crimped case mouths onto their bullets. And their rounds single loaded often have so little neck grip on the bullets, one can easily pull out a bullet with their fingers.; proving a tight grip by the case mouth on the bullet is not needed. If you've got the stuff to measure the force needed to pull a bullet out of a case, you will learn crimped in bullets have a greater spread of that force; therefore, so will velocity and pressure have greater spreads.</p><p></p><p>Sierra Bullets proved crimping reduced accuracy back in the '50's along with benchrest folks; both shooting bullets the most accurate. I think Sierra was one of the two bullet companies who got on Richard Lee about his factory crimp die causing their bullets to shoot less accurate. Lee finally agreed to put words in print saying not to crimp those makes of bullets.</p><p></p><p>Being the first person on earth to shoot an M16 across the standard course of fire in the 1971 DCM Excellence in Competition match at the Nationals, I can attest to the conversations several of us on the military teams shooting them. We all knew that many folks would want to crimp case mouths on ammo for it, but we all knew better. None of our ammo had crimped in bullets.</p><p></p><p>Arsenals used to crimp all .30-06 match ammo. I think it was Col,'s Hatcher or Townsend that convinced them to quit crimping ammo and no longer put the cannelure in that original machine gun round's 173-gr. FMJBT bullet. When they finally did that, the largest test groups got smaller. No more 30 caliber match ammo hand crimped in bullets.</p><p></p><p>Sierra Bullets caved into customer demand for their 22 caliber 77-gr. HPMK bullet to have a cannelure in it for crimping for use in AR platforms. They repeated their early '50's tests with different amounts of crimps on them as well as no crimps at all. They never crimped another test round testing that bullet for accuracy standards. Good lots of them would shoot 1/4 MOA in their 200 yard test range. Best accuracy with any crimp put 'em into 2/3 MOA at best.</p><p></p><p>Therefore, I suggest people do what they want to. Follow the trail match winners and record setters blazed with no crimped in bullets or hack your way through the woods and end up some place else.</p><p></p><p>Judge accuracy by the largest groups shot with any process of bullet seating; they happen when all the variables add up in different directions. The smallest groups are mostly luck as all the variables tend to cancel each other out. Both happen at the same low percentage rate across all groups fired anyway. They all are somewhere between some unit of measurement and zero. </p><p></p><p>Shoot at least 20 or more shots per test group to get statistically significant results. If you use the smallest single few-shot group to asses accuracy, any combination of tools and their use, components and their assembly, any given method may well be the one you prefer.</p><p></p><p>Finally, if you're not shooting your stuff into sub 1/2 MOA accuracy at worst, you may not see how much accuracy loss is caused by crimping case mouths into bullets. Even the slightest amount of crimp is enough to deform bullet jackets enough to cause imbalance at 150,000 rpm or more that makes them jump further than normal off the bore axis upon exit from the barrel.</p></blockquote><p></p>
[QUOTE="Bart B, post: 1131612, member: 5302"] For what it's worth, people winning the big matches and setting records in NRA and CMP matches shooting AR platforms using the .223/5.56 round never ever crimped case mouths onto their bullets. And their rounds single loaded often have so little neck grip on the bullets, one can easily pull out a bullet with their fingers.; proving a tight grip by the case mouth on the bullet is not needed. If you've got the stuff to measure the force needed to pull a bullet out of a case, you will learn crimped in bullets have a greater spread of that force; therefore, so will velocity and pressure have greater spreads. Sierra Bullets proved crimping reduced accuracy back in the '50's along with benchrest folks; both shooting bullets the most accurate. I think Sierra was one of the two bullet companies who got on Richard Lee about his factory crimp die causing their bullets to shoot less accurate. Lee finally agreed to put words in print saying not to crimp those makes of bullets. Being the first person on earth to shoot an M16 across the standard course of fire in the 1971 DCM Excellence in Competition match at the Nationals, I can attest to the conversations several of us on the military teams shooting them. We all knew that many folks would want to crimp case mouths on ammo for it, but we all knew better. None of our ammo had crimped in bullets. Arsenals used to crimp all .30-06 match ammo. I think it was Col,'s Hatcher or Townsend that convinced them to quit crimping ammo and no longer put the cannelure in that original machine gun round's 173-gr. FMJBT bullet. When they finally did that, the largest test groups got smaller. No more 30 caliber match ammo hand crimped in bullets. Sierra Bullets caved into customer demand for their 22 caliber 77-gr. HPMK bullet to have a cannelure in it for crimping for use in AR platforms. They repeated their early '50's tests with different amounts of crimps on them as well as no crimps at all. They never crimped another test round testing that bullet for accuracy standards. Good lots of them would shoot 1/4 MOA in their 200 yard test range. Best accuracy with any crimp put 'em into 2/3 MOA at best. Therefore, I suggest people do what they want to. Follow the trail match winners and record setters blazed with no crimped in bullets or hack your way through the woods and end up some place else. Judge accuracy by the largest groups shot with any process of bullet seating; they happen when all the variables add up in different directions. The smallest groups are mostly luck as all the variables tend to cancel each other out. Both happen at the same low percentage rate across all groups fired anyway. They all are somewhere between some unit of measurement and zero. Shoot at least 20 or more shots per test group to get statistically significant results. If you use the smallest single few-shot group to asses accuracy, any combination of tools and their use, components and their assembly, any given method may well be the one you prefer. Finally, if you're not shooting your stuff into sub 1/2 MOA accuracy at worst, you may not see how much accuracy loss is caused by crimping case mouths into bullets. Even the slightest amount of crimp is enough to deform bullet jackets enough to cause imbalance at 150,000 rpm or more that makes them jump further than normal off the bore axis upon exit from the barrel. [/QUOTE]
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