Re: Burn Rate?
Burn rates are not so much for calibers, as they are for cartridge size and barrel length.
Cartridges seem to work the best when the case has from 75 to about 90% of the space filled up with powder. Obviously, if you were loading 32 ACP, you'd want to use a fast powder, like Bullseye, so that just a little bit would burn fast and make a lot of pressure to move the bullet. But, if you were loading 460 Weatherby, filling the case with Bullseye would make it into a bomb. But putting the amount of Bullseye needed to move the bullet the desired speed would be akin to dropping a marble into a gallon jug. Depending on how you held the gun, the powder would move all around the case. If you carried the gun, muzzle down, and then saw a lion and raise it to shoot, the powder would be down by the bullet. The primer spark would have to jump four inches to set the powder off. You don't want that. You want that almost-full case of powder, so the powder is back against the primer, for sure ignition. So you need a slower burning powder.
Then, suppose you are loading 357. You have three guns. A 2 1/2 inch Model 19, an 8 3/8 inch Model 27 and a 20 inch Rossi Model 92. If you load with a powder that has a burning rate to take advantage of that 20 rifle barrel, only about 2/3 of it will be burned in that 8 inch pistol barrel. When the bullet exits the barrel, the unburned powder will all go off at once (because it hit oxygen) with a loud BANG and a fireball. Any time you see a fireball when you shoot a gun, your burning rate was too slow for THAT gun. You shoot them same rounds in your 2 1/2 inch gun, and the BANG will rattle the windows and the fireball will light up the sky. Waaaaay too slow for that barrel.
But if you use a powder that is fast enough to take advantage of that 2 1/2 inch barrel, then the powder should be all burned up in about 6 inches of barrel, and for the last 2 of your big pistol, you are getting a little friction drag on the bullet, and it is actually starting to slow down. With the additional 12 inches of rifle barrel, you have a whole lot more friction drag, and it will actually be slower coming out of the rifle muzzle than it is with the pistol.
A heavier bullet requires a slower burning powder. To get the heavier bullet moving takes a slower pressure buildup than a lighter bullet.
So, if you were shooting a 30 Carbine, you would use a faster powder than you would with a 30/06. If you were shooting a 30/06 with a 120 grain bullet, you would use a faster powder than if shooting a 30/06 with a 220 grain bullet. If you had a 30/06 rifle with a 24 inch barrel, and a T/C Contender in ought six with a 10 inch barrel, you would use a faster powder for the Contender.
Meddle not in the affairs of dragons, for thou art crunchy, and taste good with catsup - George of Lod, Year of Our Lord 297
I always take precautions.
Beware the Evil Bullet Fairies.
Last edited by Alpo; 06-01-2009 at 03:04 PM..