PP boolits 'bumping up' - 303-25

[303Guy]

I tried two patched boolits in my 25 with a neck sized case, the first on top of 7.7gr AR2205/H4227. The rifling impressions on the rear section of the boolit were faint. The neck did not expand at all. Next, I doubled the powder charge to 15.4grs. This time the neck expanded but still no primer flattening. The rifling impressions on the boolit now extended to near the nose and the base was fully impressed. This indicates that patched boolits do 'bump up' with smokeless powders. The alloy was WW plus lead pipe and air cooled - making it quite soft. The rear section of the boolit was under groove diameter.

[yeahbub]

This indicates that patched boolits do 'bump up' with smokeless powders.

You're right, 303Guy! I never quite understood why people would claim that a boolit, accelerated at a certain rate by BP, will obturate, but a boolit accelerated at the same rate or faster by smokeless would not. Acceleration by BP is pretty sudden, but acceleration by smokeless is no Sunday drive, especially when it results in velocities much greater than with the holy black. I once saw a photo of jacketed bullets that were fired from a .357 Mag revolver with the barrel removed. After exiting the cylinder, the bases were dished and the sides were bulging as though they were cast fom loose jello. That pretty much proved that obturation does indeed occur with smokeless.

[303Guy]

That's interesting, yeahbub. Thanks for that! I wonder whether paper patched boolits produce lower pressure than J-words because copper to bore friction under pressure of obturation is greater than paper to bore friction under the same or even higher obturation pressure?! Mmmm .... ???

I do know one thing for sure - paper patching is more fun than J-words!:mrgreen:

[yeahbub]

Having driven jacketed bullets and cast through a barrel from the chamber end, the jacketeds win the dificulty contest hands down! The force required to engrave them and the friction of copper-on-steel made it something I immediately determined I would never do again unless absolutely necessary. The cast boolits weren't a picnic either, but were considerably easier as long as one used a full bore dia. tool to drive them with so it doesn't get driven through the boolit. There's a high-end barrel maker (Shilen?) that pushes jacketeds through their benchrest barrels to burnish and smooth them, and this is where I imagine the TV 400 lb gorilla spends most of his time when not making luggage commercials. It stands to reason that the trip is eased somewhat for both when they are in continuous motion, but, even with increased outward pressure due to easier obturation of the cast boolit, the resistance would generally be less for the cast. Usually. In one rather extreme example, a friend wanted to use his .357 for bowling pin shoots and still reliably knock them off the table. His answer was to swage 225+ gr boolits from soft lead and get it going as fast as he could with slow powder and a heavy crimp. It worked on the bowling pins - the soft lead stuck to them and reliably knocked them to the ground, but in his quest for max power, that column of soft lead was obturating in the case enough to tear the case in two. The forward section of the case exited the chamber with the boolit and a few were recovered in the pins and backstop bearing full-depth rifling like some unintentional half-jacketed bullet. This was not a consistent thing - the cases that came apart had seen many reloadings and we figured the heavy crimp and case cannelure on them gave the lead something to grab. We could find no damage to the bore, so it was assumed that none of the cases had been left stuck in the barrel as an obstruction to subsequent rounds. He ceased the practice and went back to more conventional loadings. In my own experience with the .45 ACP, I noticed that 200gr cast with a lot of bearing surface produced slightly flatter primers than 200gr XTPs with the same load. Another cast 200gr with a lot more ogive and less bearing surface showed slightly less pressure. As with most gun things, only experimentation wil tell.