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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Bullet RPM and performance
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<blockquote data-quote="RockyMtnMT" data-source="post: 2524466" data-attributes="member: 7999"><p>Stability/rpm is a major component to proper terminal performance. Through our testing we have figured out that ballistic stability and terminal stability are two diff things. The stability calculators will calculate ballistic stability. Basically, how much spin is required for a given projectile to pass through the atmosphere without upset. Has nothing to do with after impact. There is no calculator for terminal performance. Over time we have come up with our minimum required twist for Hammer Bullets. This revolves around terminal performance. We use the Miller formula calculated at standard atmosphere at sea level for 1.5 sg as the minimum for hunting. Higher stability/rpm is better for terminal performance. This will keep the bullet oriented forward longer after impact for deeper straight line penetration. I personally like my hunting rig running closer to 2.0 sg at sea level to ensure proper terminal performance and deep straight line penetration.</p><p></p><p>There is a line of too much twist for any bullet. Jacketed bullets struggle with separation of the core from the jacket if spin is too high. Resulting in failure. We have yet to find the line of too much twist for Hammers. There has to be a line, we just haven't reached out yet. Since they are pure copper there is no separation issue. The only issue I can foresee would be bullet slipping in the rifling. So far out PDR drive band technology has not failed. The only down side to faster twist that we have seen is with heavier larger calibers with lots of horsepower causing more rifle torque. Like running 400g .375 cal bullets over 3000 fps in an 8" twist. You wind up having to hang onto the rifle more to control it. It doesn't come into play with lighter bullets.</p></blockquote><p></p>
[QUOTE="RockyMtnMT, post: 2524466, member: 7999"] Stability/rpm is a major component to proper terminal performance. Through our testing we have figured out that ballistic stability and terminal stability are two diff things. The stability calculators will calculate ballistic stability. Basically, how much spin is required for a given projectile to pass through the atmosphere without upset. Has nothing to do with after impact. There is no calculator for terminal performance. Over time we have come up with our minimum required twist for Hammer Bullets. This revolves around terminal performance. We use the Miller formula calculated at standard atmosphere at sea level for 1.5 sg as the minimum for hunting. Higher stability/rpm is better for terminal performance. This will keep the bullet oriented forward longer after impact for deeper straight line penetration. I personally like my hunting rig running closer to 2.0 sg at sea level to ensure proper terminal performance and deep straight line penetration. There is a line of too much twist for any bullet. Jacketed bullets struggle with separation of the core from the jacket if spin is too high. Resulting in failure. We have yet to find the line of too much twist for Hammers. There has to be a line, we just haven't reached out yet. Since they are pure copper there is no separation issue. The only issue I can foresee would be bullet slipping in the rifling. So far out PDR drive band technology has not failed. The only down side to faster twist that we have seen is with heavier larger calibers with lots of horsepower causing more rifle torque. Like running 400g .375 cal bullets over 3000 fps in an 8" twist. You wind up having to hang onto the rifle more to control it. It doesn't come into play with lighter bullets. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Bullet RPM and performance
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