Originally Posted by bigngreen
Why does slowing the twist or just adding a few thou to the jacket ,with no exterior design change, help if this is what was happening?
I dont have all the answers to exterior ballistics but one of the reasons for a slower twist and increased accuracy could be
1- magnus effect. the faster a bullet leaves the barrel the higher the rpm it is spinning at. at 3200 fps and 1/9.5 a bullet is spinning at 242496 rpm, at 3200 fps and 1/11 is spinning at 209280. think of a top spinning it fights gravity and wants to "stand up" The more the bullet stands the harder it is to predict the shockwave/pressure areas and the more they will change with atmospherics. the slower the spin the more the bullet will want to lie parallel to the direction it is traveling. This helps with wind effects also.
a bullet coming apart would probably start in the chamber under high pressures and may not directly correlate to velocities but may also relate to twist rate as faster rates cause higher pressures. a thicker jacket may help with this.