zimmerstutzen said:
Black powder has a longer pressure curve than smokeless. It builds slower. In the Guns and Ammo test mentioned above, if it was done with smokeless, it has absolutely no relevance to black powder shooting.
As long as there is pressure behind the ball to keep accelerating it behind the ball, velocity will increase. Some people think that black powder is entirely burned within a few inches of the breech. It isn't. if it was there could never be any flame in muzzle flash. There comes a point in increasing powder charges that the fouling left behind increases significantly over lower charges. As it was explained to me many years ago, black powder burns more completely under pressure. When the pressure is releases, the burning is less complete, leaving more fouling. So if the ball exits the muzzle while significant burning is still taking place the fouling increases dramatically.Any body that ever tried shooting unpatched balls knows the fouling builds up much much faster. a factor of powder burning under less pressure. Lyman published a book with pressures for various loads in various length barrels and the figures when comparing pressures and velocity don't necessarily correlate to higher velocity in the shorter barrels. If all the powder is burned in the first 6 to 12 inches, then pressure measurements between long and short barrels should be equal. They simply aren't. Especially given the copper crush method used in their tests. It didn't measure pressure at a particular down barrel point, but just measured max pressure. If as some surmise, the pressure is always equal in the first 6 to 12 inches, the measurements would have to be equal as well. Since the maximum pressure measurements are not equal, then powder must be continuing to burn beyond that point in the balls travel down bore.
I have seen the BP curve for a 50-140. This was done through a NRA Grant to study duplex.
It has been written by a person who did some pressure testing with BP that in some ways its like a fast pistol powder with its rapid initial acceleration and like a much slower powder due to its longer pressure curve.
Pressure is always highest just as the bullet starts to move or during initial acceleration. As the bullet moves away it increases the bore volume at an increasing rapid rate. Progressive nitro powders are designed to keep the pressure high for longer periods. But even then a cartridge like the 5.56 nato develops about 55000 psi chamber pressure but has fallen to 13000-13600 at the port.
If smokeless is fired in too short a barrel even a relatively fast powder like Unique will produce almost no velocity. A standard velocity load of Unique fired from a SAA Colt 44-40 with the barrel removed will hardly dent a 3/4" particle board.
Loaded with blackpowder the bullet will punch through the first board and seriously dent the second. Across a card table it would be a argument stopper.
So like the statement above BP has some attributes of a fast powder and some of a slow powder. I.E. it does both.
The initial acceleration of BP is pretty violent and will actually upset the bullet before it starts to move. This is why the various BP bullets can be used when under bore size. The minie ball is an example. Eventually, about the time the Minie became obsolete, it was found that the hollow base was not needed either. BP will bump up long bullets as hard as 1:16- 1:14.
Round balls, the smaller ones at least, have far less inertia and don't bump up much if at all it would seem.
I also know that 37 gr of FFF in a 38-40 case will move a 180 gr bullet out of a 4 3/4" Colt Bisley at almost 1000 fps.
Unpatched balls foul more because the patch is not there the wipe the bore between shots and some lubes will reduce fouling build upand/or soften the fouling.
A large percentage of BP does not burn and this is where the fouling comes from. Some is deposited in the bore some is ejected from the muzzle with the projectile. The
The flash at the muzzle is made up of solid remnants of combustion, fouling at near 2000 degrees and hot gases.
Dan