HenryC460
04-09-2011, 10:01 AM
I'm wondering about a statement I have seen written in a couple of places. It goes like this:
Bullets for black powder cartridge are sized bore diameter (or somewhat below groove diameter at least), because the fouling from the first shot or two would keep a groove diameter sized bullet from chambering. (The argument continues that) this is alright, because the pressure curve for black powder is something special. Pressure builds, (it is argued), in a way that bumps the bullet up to groove diameter and this makes a seal against hot gases leaking past.
Hand-in-hand with that argument about black powder is the following argument about smokeless:
But you can't get away with bore-size bullets in a smokeless cartridge, because smokeless doesn't bump bullets up to groove diameter, and the gases leak past like a cutting torch and cause problems. You must start with groove diameter or even 0.001" larger (says the argument's partner).
That may be the case. Some day, they're gonna sell crystal clear fused quartz barrels, and some guy with a high speed video camera is going to settle this once and for all. I'm just wondering.
Now, I don't want to argue about relative pressure curves. If someone else wants to argue about them, that's great. I don't, because I'm ignorant. These pressure curves are probably known. I've got me a Pressure Trace device, and if that dude on eBay hadn't sold me a non-working laptop, I'd be able to hook it up and measure the pressure curves. Anybody who's got the data or has seen it, I would be just tickled to hear about it. If that solves everything, I have one less thing I need to worry about in this world.
Here's the part of the problem that keeps me scratching my head. Why do we have to compress the black powder before we seat the bullet?
I'm thinking that maybe black powder burns differently than smokeless. Maybe it burns like a very rapidly smoked cigar, from one end to the other. Or like a solid rocket engine. Maybe the powder nearest the primer gets lit and the rest gets pushed like a plug down the bore, burning like a solid rocket behind the bullet, and maybe the powder that's waiting to be burned is what provides the seal against all that hot smoke getting past the bullet and causing problems. You can blow gas through a small orifice (like the space between the bore sized bullet and the groove-sized rifling groove), but it's pretty near impossible to ram a powdered solid through.
But if recovered bullets have rifling marks on them, does that mean I just wasted 15 minutes of my life typing this? (I type slow).
I'm not sure. It's one thing for a bullet to go from zero to 1100 f.p.s in the time it takes your rifle to say "bang." That at least provides time (4 or 5 milliseconds anyway) for the lead to squish out and conform. It's another thing for a seated solid lead bullet at rest to received such an impulse from the hot gases behind it to deform so fast that it fills the grooves before any of the gas can get past.
Does any of that make sense? What if smokeless powder burns like a hot, churning, flaming dust storm in the chamber, requiring a groove-sized bullet to keep it from leaking past, and what if black powder burns like a traveling cigar, providing the push and (initially at least) the seal?
Bullets for black powder cartridge are sized bore diameter (or somewhat below groove diameter at least), because the fouling from the first shot or two would keep a groove diameter sized bullet from chambering. (The argument continues that) this is alright, because the pressure curve for black powder is something special. Pressure builds, (it is argued), in a way that bumps the bullet up to groove diameter and this makes a seal against hot gases leaking past.
Hand-in-hand with that argument about black powder is the following argument about smokeless:
But you can't get away with bore-size bullets in a smokeless cartridge, because smokeless doesn't bump bullets up to groove diameter, and the gases leak past like a cutting torch and cause problems. You must start with groove diameter or even 0.001" larger (says the argument's partner).
That may be the case. Some day, they're gonna sell crystal clear fused quartz barrels, and some guy with a high speed video camera is going to settle this once and for all. I'm just wondering.
Now, I don't want to argue about relative pressure curves. If someone else wants to argue about them, that's great. I don't, because I'm ignorant. These pressure curves are probably known. I've got me a Pressure Trace device, and if that dude on eBay hadn't sold me a non-working laptop, I'd be able to hook it up and measure the pressure curves. Anybody who's got the data or has seen it, I would be just tickled to hear about it. If that solves everything, I have one less thing I need to worry about in this world.
Here's the part of the problem that keeps me scratching my head. Why do we have to compress the black powder before we seat the bullet?
I'm thinking that maybe black powder burns differently than smokeless. Maybe it burns like a very rapidly smoked cigar, from one end to the other. Or like a solid rocket engine. Maybe the powder nearest the primer gets lit and the rest gets pushed like a plug down the bore, burning like a solid rocket behind the bullet, and maybe the powder that's waiting to be burned is what provides the seal against all that hot smoke getting past the bullet and causing problems. You can blow gas through a small orifice (like the space between the bore sized bullet and the groove-sized rifling groove), but it's pretty near impossible to ram a powdered solid through.
But if recovered bullets have rifling marks on them, does that mean I just wasted 15 minutes of my life typing this? (I type slow).
I'm not sure. It's one thing for a bullet to go from zero to 1100 f.p.s in the time it takes your rifle to say "bang." That at least provides time (4 or 5 milliseconds anyway) for the lead to squish out and conform. It's another thing for a seated solid lead bullet at rest to received such an impulse from the hot gases behind it to deform so fast that it fills the grooves before any of the gas can get past.
Does any of that make sense? What if smokeless powder burns like a hot, churning, flaming dust storm in the chamber, requiring a groove-sized bullet to keep it from leaking past, and what if black powder burns like a traveling cigar, providing the push and (initially at least) the seal?