B Litz discusses this maximum velocity situation. He actually attributes projectile failure to heat transfer. When the lead starts to get molten, it separates from the jacket, which causes catastrophic failure in flight.
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Maximum velocity for lead core projectiles is 300,000 rpm.
Projectile maximum velocity calculation formula:
Muzzle velocity x 720 divided by barrel twist rate.
Example: 3,000 fps x 720 = 2,160,000 / 8 twist = 270,000 rpm
You can also use this to find maximum velocity:
300,000 rpm x 8 twist / 720...