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A while back I talked to some guys about pressure signs and the topic of the bulged case came up. Seems that most of the time, you will see a bulged case right near the head on a case. Now the brass isn't any thinner there than elsewhere, so we got into disussing what was going on to cause that.
Well the consensus was that at the instant the primer is ignited and the first bit of powder ignites, not only is the weight of the bullet keeping the pressure confined, but also the weight of the powder that has yet started burning is a factor. As added evidence, barrel makers will tell you that throat erosion on a barrel is often caused by unburned powder sand blasting that front part of the barrel and starting point of the rifling. So this seems to indicate that a good bit of powder is being thrown up through the barrel before it finally gets lit afire.
Take a .50BMG cartridge, for instance. When the primer first ignites, there is not only the 650 to 800 grain projectile sitting on top of that first pressure wave, but there is also around 220 grains of powder sitting on top of it as well.
So is the basic design of a centerfire cartidge just wrong, or at least highly inefficient? Wouldn't it be better to have a design that would do a controlled burn of the powder from the FRONT (near the projectile) which would tend to utilize only expanding gas to push the bullet out the barrel? Since the powder would be burning back towards the head of the case, there would not be any case of the weight of the unburned powder being a factor in the pressure curve.
Yeah, this is all ivory tower thinking, and trying to come up with a new cartridge design that would work this way would probably be very difficult to do. New technology has advanced to electronic igniting systems now, and the impact initiated primer really is no longer a necessity.
How were the caseless projectiles ignited? Weren't they just basically a block of powder with a primer embedded in them? Whatever happened to them anyway?
Anyway, just some idle speculation on a Sunday afternoon....
Well the consensus was that at the instant the primer is ignited and the first bit of powder ignites, not only is the weight of the bullet keeping the pressure confined, but also the weight of the powder that has yet started burning is a factor. As added evidence, barrel makers will tell you that throat erosion on a barrel is often caused by unburned powder sand blasting that front part of the barrel and starting point of the rifling. So this seems to indicate that a good bit of powder is being thrown up through the barrel before it finally gets lit afire.
Take a .50BMG cartridge, for instance. When the primer first ignites, there is not only the 650 to 800 grain projectile sitting on top of that first pressure wave, but there is also around 220 grains of powder sitting on top of it as well.
So is the basic design of a centerfire cartidge just wrong, or at least highly inefficient? Wouldn't it be better to have a design that would do a controlled burn of the powder from the FRONT (near the projectile) which would tend to utilize only expanding gas to push the bullet out the barrel? Since the powder would be burning back towards the head of the case, there would not be any case of the weight of the unburned powder being a factor in the pressure curve.
Yeah, this is all ivory tower thinking, and trying to come up with a new cartridge design that would work this way would probably be very difficult to do. New technology has advanced to electronic igniting systems now, and the impact initiated primer really is no longer a necessity.
How were the caseless projectiles ignited? Weren't they just basically a block of powder with a primer embedded in them? Whatever happened to them anyway?
Anyway, just some idle speculation on a Sunday afternoon....