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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Bullet Spin and Performance
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<blockquote data-quote="Fiftydriver" data-source="post: 248588" data-attributes="member: 10"><p>LV,</p><p> </p><p>Your question about how groove count is a very interesting one.</p><p> </p><p>I have done some studying on this as well, more by accident then intentional but none the less. I shot a whitetail at 750 yards with the 200 gr ULD RBBT 7mm wildcat bullet. The deer was hit on the onside shoulder on a slight quartering toward me angle. Ran 30 yards and fell over dead. </p><p> </p><p>I got full penetration on the deer but she was standing on a game trail with a relatively steep bank behind her and luckily it was pretty clean dirt. As luck would have it, I was able to recover the exanded bullet. </p><p> </p><p>I found parts of the core and most of the jacket which looked kind of strange as it had 4 major petals on the expanded bullet. When I got to looking at this, the bullet jacket expanded and seperated along the lead edge of each of the land engavings..... Being a 4 groove Lilja barrel.</p><p> </p><p>Seeing this I started checking to see how this effected expansion on different bullet.</p><p> </p><p>On the Berger, Wildcat and A-Max bullets it seemed to be pretty common for this to happen. With the SMK, it never made any difference from what I could see and on the Accubond there was also no sign of any predictable jacket cutting locations, instead it appeared to roll back over itself more like a sock.</p><p> </p><p>Seeing this, I believe that with the thin jacketed bullets, this can be an issue.</p><p> </p><p>I took this a bit further and tested in a 6 groove 1-9 as well as a 3 groove 1-7.</p><p> </p><p>In most cases, out of the 7mm AM, the 1-7 twist ripped the Berger, A-max and Wildcats apart. The Accubonds performed the same way as the 4 groove barrel.</p><p> </p><p>The 6 groove barrel shot all bullets very well and there did not seem to be any distinct jacket expansion along the land engraving edge.</p><p> </p><p>As far as accuracy and expansion, there was not a dramatic difference that could be measured, at least in the bullets that could survive testing in all twist rates and groove counts.</p><p> </p><p>One interesting point, when the 1-7, 3 groove barrels got around 250-300 rounds down the barrels, they started dusting all the thin jacketed bullets no matter what velocity they were driven to. I tested from 2800 to 3400 fps, did not matter all dusted. </p><p> </p><p>From new to that point, these barrels were shooting WELL under 1/2 moa with all bullets so this tells me that the bullets were on the ragged edge and when the bores got just a bit of wear on them to rough them up a bit, it was more then these bullets could take.</p><p> </p><p>The same bullets in the 1-9 4 groove barrels, have never had this problem at all unless you push them over 3300 fps. I am referring to the 180 gr Berger and 200 gr ULD RBBT.</p></blockquote><p></p>
[QUOTE="Fiftydriver, post: 248588, member: 10"] LV, Your question about how groove count is a very interesting one. I have done some studying on this as well, more by accident then intentional but none the less. I shot a whitetail at 750 yards with the 200 gr ULD RBBT 7mm wildcat bullet. The deer was hit on the onside shoulder on a slight quartering toward me angle. Ran 30 yards and fell over dead. I got full penetration on the deer but she was standing on a game trail with a relatively steep bank behind her and luckily it was pretty clean dirt. As luck would have it, I was able to recover the exanded bullet. I found parts of the core and most of the jacket which looked kind of strange as it had 4 major petals on the expanded bullet. When I got to looking at this, the bullet jacket expanded and seperated along the lead edge of each of the land engavings..... Being a 4 groove Lilja barrel. Seeing this I started checking to see how this effected expansion on different bullet. On the Berger, Wildcat and A-Max bullets it seemed to be pretty common for this to happen. With the SMK, it never made any difference from what I could see and on the Accubond there was also no sign of any predictable jacket cutting locations, instead it appeared to roll back over itself more like a sock. Seeing this, I believe that with the thin jacketed bullets, this can be an issue. I took this a bit further and tested in a 6 groove 1-9 as well as a 3 groove 1-7. In most cases, out of the 7mm AM, the 1-7 twist ripped the Berger, A-max and Wildcats apart. The Accubonds performed the same way as the 4 groove barrel. The 6 groove barrel shot all bullets very well and there did not seem to be any distinct jacket expansion along the land engraving edge. As far as accuracy and expansion, there was not a dramatic difference that could be measured, at least in the bullets that could survive testing in all twist rates and groove counts. One interesting point, when the 1-7, 3 groove barrels got around 250-300 rounds down the barrels, they started dusting all the thin jacketed bullets no matter what velocity they were driven to. I tested from 2800 to 3400 fps, did not matter all dusted. From new to that point, these barrels were shooting WELL under 1/2 moa with all bullets so this tells me that the bullets were on the ragged edge and when the bores got just a bit of wear on them to rough them up a bit, it was more then these bullets could take. The same bullets in the 1-9 4 groove barrels, have never had this problem at all unless you push them over 3300 fps. I am referring to the 180 gr Berger and 200 gr ULD RBBT. [/QUOTE]
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