Thoughts and Observations!
Concerning the shooting of all-lead cast PP bullets.....here's something that I THINK I know! When the powder ignites...all hell breaks loose inside the barrel, the **** end of the bullet gets hit in a nanosecond with tons of pressure...and the nose is the first thing that moves....REARWARD! At the same time the nose is moving slightly rearward the exterior of the bullet is being blown outward against the interior of the barrel and the nose of the projectile has several tons of torque applied to it attempting to twist it out of it's structural integrity. Shortly after being 'pressure cooked'....the projectile is again exposed to being hammered when it gets to within about 6" of exiting the muzzle because it's being squeezed down by the choke within those last 6" prior to exiting the muzzle!
When you stop to think about it.....it's a damn good thing lead does have elasticity to a degree because without it we wouldn't be able to hit a frickin barn! And all the more reason for being able to select an alloy that best withstands all the labors that a cast bullet is subjected to and all the more reason for being able to cast good bullets!