Internal ballistics

[USSR]

Assuming a .30 caliber PB cast bullet being fired in a .30 Carbine and two powders being considered, one relatively fast (2400), and the other relatively slow (IMR4227), are there any advantages or disadvantages to a more rapid rise in pressure or a slower rise in pressure in regards to a PB cast bullet?

Don

[runfiverun]

obduration,lube and boolit composition
i'd probably go with the 2400

[Larry Gibson]

Well, I've tried both powders with Lyman's 311410 in several M1 Carbines. Both powders delivered so-so accuracy in the 1500 fps range. Both powders delivered poor accuracy (actually the culprit was the PB bullet) above that. With lighter bullets like 31118 it was the same story; both giving so-so accuracy at 1500 fps range and poor accuracy above that. If you want good accuracy at .30 carbine velocities then use a GC'd bullet of 1005-125 gr.

Larry Gibson

[cbrick]

Different schools of thought on this, I've always looked at it this way. Here's the boolit sitting happily in its case mouth in the chamber, its about to be flying out the muzzle at X velocity. Which is better for not only the base but the entire bullet, pressure starts, bullet moves a bit, pressure still building and the bullet begins moving faster and faster as pressure is building behind it until it reaches its max velocity at or near the muzzle. The other scenario with fast powder is the boolit sitting happily in its case mouth in the chamber, its about to be flying out the muzzle at X velocity and to reach this velocity its whacked in the ass by a sledge hammer.

OK, that's an over generalization but it does get the point across. I've always been a fan of the slowest powder that you can get enough in the case that will give you the desired velocity when trying to increase velocity or for upper end loads.

Rick