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Fast rate of twist?
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<blockquote data-quote="VinceMule" data-source="post: 2791672" data-attributes="member: 122164"><p>The proper twist rate for your bullet is how I roll. If the twist is much faster than my bullet, the bullet may not "go to sleep" for 200 yards, in which case the Bullet Yaw decreases that BC.</p><p></p><p>Much work has been done to get a bullet to go to sleep as quickly as it can out of the barrel, eliminating as much bullet yaw as possible.</p><p></p><p>Twisting the fastest rate possible due to the fact that one day you may wake up and decide what you really want drives you to shoot heavy for twist rate bullets, whether or not you want to go there or not.</p><p></p><p>For example, when I want to shoot 140g-150g cup and core bullets in my 7 mags and 7 sTW, I shoot an 11 twist and three grooves. This is going to drop pressure while boosting velocity. The same thing applies to 30-cal hunting bullets, you slow the RPMs down, and they penetrate better, so lighter bullets perform in some respects like heavier bullets.</p><p></p><p>All of the twist rate recommendations are steeped in Traditions, but when you start actually using a twist rate calculator, the learning curve is quite impressive. The Berger Bullet website can give you a glimpse into what is necessary on the twist rate for a particular bullet.</p><p></p><p> Very fast Bullet RPM makes bullet jackets open up faster(316,000+), we have seen this over and over again on varmint rigs. So, do you want your big game bullet to blow up quicker in an animal, then twist if faster? This may also introduce bullets blowing up prematurely, especially in barrels with cracking in the bore and rough finish due to heat/ pressure.</p><p></p><p>In the 6.5 caliber, the 147g and in the 7mm, the 180g eldms are famous for blowing up when twisted too fast or shot too hard. The Engraving pressure as the bullet enters the lands is tremendous with the pressure spike that accompanies it, and controlling bullet base deformation is critical.</p><p></p><p> Berger had one heck of a time with his first 6mm 105's when they came out due to boat tails deforming during obturation as pictures taken by Bill Davis at Aberdine Proving Grounds showed. They changed the alloy mix which cured the problem-Olympic Comp bullets.</p><p></p><p>In the 22 caliber, 6.5 twist is needed for hot weather with 90g Bergers, and throat accordingly, which means the use of lighter bullets you should consider a crap shoot.</p><p></p><p>Prudent to take a step back, Use a ballistics calculator, plug in your bullet, velocity, and temp, and see what gives you a 1.5 stabilization factor, with a 1.2 being marginal during certain weather and elevations. When shooting hot rod cartridges, I always use a slower-than-normal twist, I am looking for that magic RPM rate that I want given the velocity of the cartridge, elevation, temp, etc.</p><p></p><p>I do not shoot monos as a rule with the exception of 110g Barnes ttsx in my 270, 80g ttsx in a 257 Weatherby, and 80g TTSX in a 243 win.</p></blockquote><p></p>
[QUOTE="VinceMule, post: 2791672, member: 122164"] The proper twist rate for your bullet is how I roll. If the twist is much faster than my bullet, the bullet may not "go to sleep" for 200 yards, in which case the Bullet Yaw decreases that BC. Much work has been done to get a bullet to go to sleep as quickly as it can out of the barrel, eliminating as much bullet yaw as possible. Twisting the fastest rate possible due to the fact that one day you may wake up and decide what you really want drives you to shoot heavy for twist rate bullets, whether or not you want to go there or not. For example, when I want to shoot 140g-150g cup and core bullets in my 7 mags and 7 sTW, I shoot an 11 twist and three grooves. This is going to drop pressure while boosting velocity. The same thing applies to 30-cal hunting bullets, you slow the RPMs down, and they penetrate better, so lighter bullets perform in some respects like heavier bullets. All of the twist rate recommendations are steeped in Traditions, but when you start actually using a twist rate calculator, the learning curve is quite impressive. The Berger Bullet website can give you a glimpse into what is necessary on the twist rate for a particular bullet. Very fast Bullet RPM makes bullet jackets open up faster(316,000+), we have seen this over and over again on varmint rigs. So, do you want your big game bullet to blow up quicker in an animal, then twist if faster? This may also introduce bullets blowing up prematurely, especially in barrels with cracking in the bore and rough finish due to heat/ pressure. In the 6.5 caliber, the 147g and in the 7mm, the 180g eldms are famous for blowing up when twisted too fast or shot too hard. The Engraving pressure as the bullet enters the lands is tremendous with the pressure spike that accompanies it, and controlling bullet base deformation is critical. Berger had one heck of a time with his first 6mm 105's when they came out due to boat tails deforming during obturation as pictures taken by Bill Davis at Aberdine Proving Grounds showed. They changed the alloy mix which cured the problem-Olympic Comp bullets. In the 22 caliber, 6.5 twist is needed for hot weather with 90g Bergers, and throat accordingly, which means the use of lighter bullets you should consider a crap shoot. Prudent to take a step back, Use a ballistics calculator, plug in your bullet, velocity, and temp, and see what gives you a 1.5 stabilization factor, with a 1.2 being marginal during certain weather and elevations. When shooting hot rod cartridges, I always use a slower-than-normal twist, I am looking for that magic RPM rate that I want given the velocity of the cartridge, elevation, temp, etc. I do not shoot monos as a rule with the exception of 110g Barnes ttsx in my 270, 80g ttsx in a 257 Weatherby, and 80g TTSX in a 243 win. [/QUOTE]
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