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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
6.5 SAUM, 6.5 Creedmoor, 7mm-08
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<blockquote data-quote="57K" data-source="post: 1354752" data-attributes="member: 75296"><p>5RWill, I'm thinking the ability to load bullets further out of the neck would have the same advantage it does with the 6.5 CM and hopefully the 6.5 PRC. And maybe performance equal to the .280 AI. The twist rate would likely be the same or close to 1 in 9.5".</p><p></p><p>Since these rounds are shorter versions of an already "short magnum" and sill longer than the SSMs, I'm not much concerned about labeling. But your point is well taken. It would require a "magnum" bolt-face. Really the only necessary mod other than the appropriate chamber. That might make it more attractive to rifle-makers.</p><p></p><p>Dealing with pressure is part of my vocation, so the points about pressure nodes are well taken. I would like to see if a 7mm PRC would be the equal of the .280 AI at 52,000 CUP/62,000 PSI where many of the short magnums are rated 65,000 PSI and previously 54,000 CUP.</p><p></p><p>I'm sure there are guys here who know more than I do. A 1 in 8" twist rate for the 6.5 CM and .260 Rem might be the ticket. Then twists for older 6.5 x 55mm Swedish Mausers are even faster. I really don't know how much thought cartridge designers have put into this. My SPEER #11 load manual states that 45,000 PSI is max for 94 Swedes and that start charges should be considered max for the 94s. The twist rate there was 1 in 7.5". So, if the Swede can handle warmer loads with modern bolt rifles, it seems that the twist rate should be appropriate for velocity gains. That is exactly what CZ does with their 550 models chambered in 6.5 x 55mm @ 1 in 8.75" or thereabouts. I'm not so concerned about stabilization as I am the consideration of pressure.</p><p></p><p>We know that time is a function of pressure measurement, so obviously time in bore, or dwell time will be longer in a faster twist barrel. And I realize we're talking micro-seconds here. But still, I wonder if 1 in 8" is the right twist for 6.5s faster and warmer in pressure than the 6.5 CM and .260 Rem. And with the longer dwell time/higher pressure comes higher burn temps of the propellant charge. Just my hypothesis, but I believe some of these short-lived barrel issues could be helped somewhat with slower twists where calculators like Berger's would show plenty of stabilization with slightly slower twists. I can't say if CZ was aware of this when they gave the 550 a 1 in 8.75" twist, but I suspect it was, and done so for those who load to modern pressure levels that the cartridge case is capable of.</p><p></p><p>With fairly minimal cost differences, 7mm-08s could be manufactured for 7mm PRC and hopefully with 24" barrels for sporters, Customs at 26". This for mass produced rifles. That is essentially what's done for 7mm WSM and it's been some time since I've seen a 7mm SAUM in anyone's catalog except for maybe Remington's. That would also remove any proprietary cartridge envy, for lack of a better term.</p><p></p><p>The differences in powder charge weight for 7mm-08 and 7mm WSM are not so great if say you look at a 150 gr. bullet. And true, start charges for the 7mm WSM are close to 7mm-08 performance. Hopefully, the 7mm PRC would be about midway in-between. I think it could be a great combination cartridge.</p><p></p><p>Sorry for being long-winded, but getting back to the OPs question in case it hasn't been resolved, I'm like the poster who mentioned his 7mm-08 150 gr. Handload at 2900 FPS vs around 2750 FPS with a 140 in the 6.5 CM or .260 Rem. That's why I'd go with a 7mm-08 over either and probably more from a hunting perspective. But, the 7mm-08 was also born from rifle competition (Silhouette).</p></blockquote><p></p>
[QUOTE="57K, post: 1354752, member: 75296"] 5RWill, I'm thinking the ability to load bullets further out of the neck would have the same advantage it does with the 6.5 CM and hopefully the 6.5 PRC. And maybe performance equal to the .280 AI. The twist rate would likely be the same or close to 1 in 9.5". Since these rounds are shorter versions of an already "short magnum" and sill longer than the SSMs, I'm not much concerned about labeling. But your point is well taken. It would require a "magnum" bolt-face. Really the only necessary mod other than the appropriate chamber. That might make it more attractive to rifle-makers. Dealing with pressure is part of my vocation, so the points about pressure nodes are well taken. I would like to see if a 7mm PRC would be the equal of the .280 AI at 52,000 CUP/62,000 PSI where many of the short magnums are rated 65,000 PSI and previously 54,000 CUP. I'm sure there are guys here who know more than I do. A 1 in 8" twist rate for the 6.5 CM and .260 Rem might be the ticket. Then twists for older 6.5 x 55mm Swedish Mausers are even faster. I really don't know how much thought cartridge designers have put into this. My SPEER #11 load manual states that 45,000 PSI is max for 94 Swedes and that start charges should be considered max for the 94s. The twist rate there was 1 in 7.5". So, if the Swede can handle warmer loads with modern bolt rifles, it seems that the twist rate should be appropriate for velocity gains. That is exactly what CZ does with their 550 models chambered in 6.5 x 55mm @ 1 in 8.75" or thereabouts. I'm not so concerned about stabilization as I am the consideration of pressure. We know that time is a function of pressure measurement, so obviously time in bore, or dwell time will be longer in a faster twist barrel. And I realize we're talking micro-seconds here. But still, I wonder if 1 in 8" is the right twist for 6.5s faster and warmer in pressure than the 6.5 CM and .260 Rem. And with the longer dwell time/higher pressure comes higher burn temps of the propellant charge. Just my hypothesis, but I believe some of these short-lived barrel issues could be helped somewhat with slower twists where calculators like Berger's would show plenty of stabilization with slightly slower twists. I can't say if CZ was aware of this when they gave the 550 a 1 in 8.75" twist, but I suspect it was, and done so for those who load to modern pressure levels that the cartridge case is capable of. With fairly minimal cost differences, 7mm-08s could be manufactured for 7mm PRC and hopefully with 24" barrels for sporters, Customs at 26". This for mass produced rifles. That is essentially what's done for 7mm WSM and it's been some time since I've seen a 7mm SAUM in anyone's catalog except for maybe Remington's. That would also remove any proprietary cartridge envy, for lack of a better term. The differences in powder charge weight for 7mm-08 and 7mm WSM are not so great if say you look at a 150 gr. bullet. And true, start charges for the 7mm WSM are close to 7mm-08 performance. Hopefully, the 7mm PRC would be about midway in-between. I think it could be a great combination cartridge. Sorry for being long-winded, but getting back to the OPs question in case it hasn't been resolved, I'm like the poster who mentioned his 7mm-08 150 gr. Handload at 2900 FPS vs around 2750 FPS with a 140 in the 6.5 CM or .260 Rem. That's why I'd go with a 7mm-08 over either and probably more from a hunting perspective. But, the 7mm-08 was also born from rifle competition (Silhouette). [/QUOTE]
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6.5 SAUM, 6.5 Creedmoor, 7mm-08
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