Something I've always wondered about high power rifles shooting copper jacketed bullets with a lead core. If you had a 12 inch twist on a barrel shooting 3000fps, then at the muzzle the bullet is spinning at 3000 revs per second, times 60 which is 180,000rpm. If its a 9 inch twist then its 240,000rpm. That means this heavy mass goes from 0 to 240,000rpm in about 2 milliseconds. That's incredible moment of inertia. Now, Lead melts at 621 degrees F and is a heavy mass, yet the copper jacket is being spun around the lead which is probably either liquid or close to it, very soft. The question to be answered is does the lead core reach melting point but I think its possible that these copper jackets are spinning around the lead core which is moving at a slower rotation. Does it cool down and match speed with the copper jacket in the next 1.5 seconds before it hits the target? I doubt it. It might even be getting hotter from the air friction. Maybe they put some baffling in the empty jacket to keep this from happening even if the lead is liquid, I don't know.
This is an interesting theory .
I happen to think along a different viewpoint about the lead cores melting inside the copper jackets .
For many years I hunted with a 7mm Remington Magnum shooting 150gr Nosler Partition bullets at a chronographed velocity of 3250 FPS average , out of a 1:9.25" twist barrel , that would mathematically achieve a rotational speed of 252,972 RPM's . THAT SHOULD GENERATE SUBSTANTIAL HEAT AND CENTRIFUGAL FORCES , according to the theory expressed above.
If you are familiar with the Nosler partition bullets , and you examine a cross-sectioned partition bullet , you will see that the copper jacket is drawn in a shape that resembles the letter H , with lead being above and below the partition , with a visibly exposed lead tip , and a visibly exposed much broader lead base with the copper jacket minimally closed around edges of the lead base to hold it in place .
I have only recovered 3 of these Partition bullets from inside animals (all others exiting) , and in all 3 recovered bullets only the jacket and rear core were found . The lead inside the rear of the Partition looked to be perfectly smooth , with no evidence of heat deformation from being exposed to the blast heat . The surface of the lead looked just as smooth and unmarked as the surface of a new Partition bullet out of a new box .
If all of this heat is generated , shouldn't the lead base have shown markings indicating the beginning of melting ?
Now , after having listed my personal experiences and observations , I will post my theory about the heat from the burning of the powder effect of heating the bullet/projectile .
I think that the bullet is being pushed/propelled out of the barrel by a pressure wave created by the burning rapidly expanding gases generated by the burning gunpowder .
When i have watched extreme slow-motion video of bullets exiting the muzzles of different firearms , the bullet is always several inches ahead of the flash/fireball of the burning powder.
THIS IS JUST MY OPINION . I am NOT trying to argue with anyone on this subject .
One final observation about the theory of the melting of the exposed soft lead tip of spitzer shaped bullets while in flight .
While hunting in the mountains of Colorado in 1984 , I once found a bullet that had fallen to earth , not having hit any animal or object , just laying on the ground . The copper jacket was scribed by the lands of the rifle barrel , and the forward tapered nose was slightly bent , flattened , and scratched on one side from falling from the sky to the earth , and the exposed soft lead tip was still there on the tip of the bullet , although bent and scratched also .
I kept this bullet as a trophy/memento from my hunting trips , and I have it stashed away somewhere .
DMP25-06