I want to better understand how cartridge length and bullet seating depth affect internal ballistics.
I understand that shortening OAL and seating a bullet deeper in the case reduces the case volume and increases the maximum pressure that will be reached after ignition. Some other factors are the bullet's resistance due to mass, diameter, composition, crimping, and how close it is to the lands, and the powder's burn rate.
Independent of those other variables, how would you describe what happens when a bullet is seated farther from the base so that OAL is increased? Two practical examples I've encountered are a shot load or ball in a smoothbore muzzleloader, and the .38 special/.357 magnum in a smoothbore revolver cylinder.
If a ball or load of shot in a smoothbore migrates down the barrel prior to ignition (possibly because of recoil produced by a double-barrel's other barrel firing), the result is a long tube containing powder closed at one end by the breech and the other end by the load. Some people have described the similarities to a pipe-bomb.
Now consider the .357 magnum. Although it's very close to the same diameter as 9mm, the case length is much greater due to the parent .38 Special's black-powder origin, and the desire to make it even longer to establish incompatibility with .38 chambers suitable for no more than 17,000 psi. The .357's SAAMI pressure limit is 35,000 psi, the same as the 9x19mm SAAMI limit.
It is well established that .357 magnum is capable of greater ballistic performance than 9x19mm, but it's obviously not because it can be loaded to higher chamber pressure. So while the case is "bigger," it's not as simple as allowing for a greater charge of powder since the .357 magnum has practically the same pressure limit. In fact, I can't see how it can be anything other than the fact .357 magnum can have the bullet seated farther away and more empty space in the case. They way I imagine that working is that it somehow allows for greater area under the pressure curve, but what other variables are needed to effect that, I'm not sure I understand.
One of the apparent advantages of .357 magnum is the versatility in bullet mass. 158, even 180 grain bullets are popular in .357 magnum, whereas the 9mm is rarely loaded over 147 grains. The greater case length and being insensitive to length with respect to magazines and feeding provide for that. But even when comparing the ballistics of cartridges using the same bullet mass (or 124 gr. vs 125 gr.), and similar or same barrel lengths, the .357 magnum tends to demonstrate unquestionably superior velocity even with the loss of some pressure from a barrel to cylinder gap.
As far as I can tell, reduced case capacity such as found in the 9x19mm tends to limit the use of high speed powders more than low speed powders. In other words, if I'm using a high burn rate powder and seating my bullet deeply, I get into overpressure condition sooner than when using a slower rate powder. I might be mistaken about this, but if this is true, then one advantage of a large case like .357 magnum would be the ability to better handle high burn rate powders. But .357 magnum tends to achieve the highest velocities with slow burn rate powders.
So given the same bullet mass, does .357 have an advantage because of the type of powders that can be utilized? Or is it just the extra case length? And how does that relate to the "pipe bomb" I described?
I understand that shortening OAL and seating a bullet deeper in the case reduces the case volume and increases the maximum pressure that will be reached after ignition. Some other factors are the bullet's resistance due to mass, diameter, composition, crimping, and how close it is to the lands, and the powder's burn rate.
Independent of those other variables, how would you describe what happens when a bullet is seated farther from the base so that OAL is increased? Two practical examples I've encountered are a shot load or ball in a smoothbore muzzleloader, and the .38 special/.357 magnum in a smoothbore revolver cylinder.
If a ball or load of shot in a smoothbore migrates down the barrel prior to ignition (possibly because of recoil produced by a double-barrel's other barrel firing), the result is a long tube containing powder closed at one end by the breech and the other end by the load. Some people have described the similarities to a pipe-bomb.
Now consider the .357 magnum. Although it's very close to the same diameter as 9mm, the case length is much greater due to the parent .38 Special's black-powder origin, and the desire to make it even longer to establish incompatibility with .38 chambers suitable for no more than 17,000 psi. The .357's SAAMI pressure limit is 35,000 psi, the same as the 9x19mm SAAMI limit.
It is well established that .357 magnum is capable of greater ballistic performance than 9x19mm, but it's obviously not because it can be loaded to higher chamber pressure. So while the case is "bigger," it's not as simple as allowing for a greater charge of powder since the .357 magnum has practically the same pressure limit. In fact, I can't see how it can be anything other than the fact .357 magnum can have the bullet seated farther away and more empty space in the case. They way I imagine that working is that it somehow allows for greater area under the pressure curve, but what other variables are needed to effect that, I'm not sure I understand.
One of the apparent advantages of .357 magnum is the versatility in bullet mass. 158, even 180 grain bullets are popular in .357 magnum, whereas the 9mm is rarely loaded over 147 grains. The greater case length and being insensitive to length with respect to magazines and feeding provide for that. But even when comparing the ballistics of cartridges using the same bullet mass (or 124 gr. vs 125 gr.), and similar or same barrel lengths, the .357 magnum tends to demonstrate unquestionably superior velocity even with the loss of some pressure from a barrel to cylinder gap.
As far as I can tell, reduced case capacity such as found in the 9x19mm tends to limit the use of high speed powders more than low speed powders. In other words, if I'm using a high burn rate powder and seating my bullet deeply, I get into overpressure condition sooner than when using a slower rate powder. I might be mistaken about this, but if this is true, then one advantage of a large case like .357 magnum would be the ability to better handle high burn rate powders. But .357 magnum tends to achieve the highest velocities with slow burn rate powders.
So given the same bullet mass, does .357 have an advantage because of the type of powders that can be utilized? Or is it just the extra case length? And how does that relate to the "pipe bomb" I described?