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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Bullet Spin and Performance
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<blockquote data-quote="Michael Eichele" data-source="post: 248390" data-attributes="member: 1007"><p>There are 2 parts to over spinning a bullet. One part is the affect on game. The other is the affects in exterior ballistics. Exterior ballistics being what happens between the muzzle and the game.</p><p></p><p>In regards to killing power, additional RPMs (greater than what is needed for PROPER stabilization) will cause several things. A greater wound chanel in game due to cyntrifical force. It creates more temporary cavitation inside the critter by way of a shock wave. this is caused by the high RPM's. The higher the RPM the greater this "shock wave". Some bullets will also shed more jacket material into the animal due to this higher RPM and subsequent cyntrifical force. </p><p></p><p>From an exterior in flight ballistics standpoint it leads to lower BCs from causing the BC to decay more rapidly and more inches of spin drift downrange. Bullets that are stabilized to a 1.5 stability factor will have the best BC potential and the least amount of spin drift. It is better to have a bullet slightly over stable than under stable but the best is 1.5 The reason we have stability factors is because it obviously takes more or less twist to stabilize a given bullet. It may take a 10 twist to stabilize a 240 SMK yet only a 12 twist for a 190. Both will have close to 1.5 stability factors here. This is where they will be at their optimum performance in the air. As far as exterior ballistics are concerned, the closer you can put a bullet to sleep to the end of your barrel the better off you will be. Note that stable and sleep are 2 totally different subjects.</p><p></p><p>To explain sleep better, all bullets have a prefered or better yet "optimum" RPM in which they will settle down and have the most perfect stabilization. This is why some rifle/bullet cominations have larger MOA patterns at closer ranges than longer ranges. In some dramatic cases, groups will be smaller at long range and larger at short range. A bullet may be over spun to a point and as the bullet decelerates finds its optimum RPM and goes to sleep. Once asleep, they typically wont wake up untill they hit the transonic wall. Some may continue on and maintain somewhat stable and others will loose everything and keyhole untill the tumble.</p></blockquote><p></p>
[QUOTE="Michael Eichele, post: 248390, member: 1007"] There are 2 parts to over spinning a bullet. One part is the affect on game. The other is the affects in exterior ballistics. Exterior ballistics being what happens between the muzzle and the game. In regards to killing power, additional RPMs (greater than what is needed for PROPER stabilization) will cause several things. A greater wound chanel in game due to cyntrifical force. It creates more temporary cavitation inside the critter by way of a shock wave. this is caused by the high RPM's. The higher the RPM the greater this "shock wave". Some bullets will also shed more jacket material into the animal due to this higher RPM and subsequent cyntrifical force. From an exterior in flight ballistics standpoint it leads to lower BCs from causing the BC to decay more rapidly and more inches of spin drift downrange. Bullets that are stabilized to a 1.5 stability factor will have the best BC potential and the least amount of spin drift. It is better to have a bullet slightly over stable than under stable but the best is 1.5 The reason we have stability factors is because it obviously takes more or less twist to stabilize a given bullet. It may take a 10 twist to stabilize a 240 SMK yet only a 12 twist for a 190. Both will have close to 1.5 stability factors here. This is where they will be at their optimum performance in the air. As far as exterior ballistics are concerned, the closer you can put a bullet to sleep to the end of your barrel the better off you will be. Note that stable and sleep are 2 totally different subjects. To explain sleep better, all bullets have a prefered or better yet "optimum" RPM in which they will settle down and have the most perfect stabilization. This is why some rifle/bullet cominations have larger MOA patterns at closer ranges than longer ranges. In some dramatic cases, groups will be smaller at long range and larger at short range. A bullet may be over spun to a point and as the bullet decelerates finds its optimum RPM and goes to sleep. Once asleep, they typically wont wake up untill they hit the transonic wall. Some may continue on and maintain somewhat stable and others will loose everything and keyhole untill the tumble. [/QUOTE]
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