Willie Sutton
Moderator
"The acceleration time for the gun is only the time from powder ignition until the bullet leaves the casing - and the gas starts expanding down the barrel."
Uhh... no. The accelleration G loads are peak when the bore velocity is peak. Bore pressure v/s bullet position in bore charts show this clearly, the peak pressure point will of course vary based on the burn rate of the propellent, etc. But pressure does not drop to zero until the bullet is long gone from the bore. Until that occurs there will be thrust rearwards which is part of felt recoil.
However, we do generally agree, and I do see your point. It's all about time. But before we go there, consider this:
The recoil pulse is present (albeit variable) until bore pressure drops to zero, which is sometime after the bullet exits the bore.
Even after the bullet reaches it's external ballistics phase, gas is being ejected from the bore until bore pressure drops to zero. This takes a discrete period of time, and during that time you can imagine it as though you are on the receiving end of a low thrust rocket engine (which is exactly what it is at that moment).The time base of the equation is the key... that goes both for the accelleration phase and the decelleration phase. One thing that soft armor does as opposed to hard armor is to lengthen the decelleration phase, thus lowering the peak loads produced. Hard armor deforms less, but the time base for decelleration of the projectile is shorter. The recipient will feel it as a sharper "crack" against the armor as opposed to a longer and softer "thump" with soft armor. Naturally we are talking milliseconds here, but in physics milliseconds are a liftime...
Double the time base and the peak G loads are reduced by a huge amount. Make the time base 10X and the the forces drop off... orders of magnitude and all... and this is what your math shows.
S0: A firearm produces X Joules of energy. By definition half is projected in one direction and the other half is projected in the opposite direction. The felt result (at either end) is all based on the mass of the system in motion and the time base over which the force is spread.
Should I run the calculus? We are getting closer and closer to my professional field of expertise....
More germane to the discussion: The keys to penetration are velocity, sectional density, geometry of the projectile, and projectile hardness. Thin, fast and hard (IE: non expanding)beats the same kinetic energy level delivered thick and slow. Sabot's shedding off of a small diameter hardened penetrator is how it's done on real armor.
Willie
.
Uhh... no. The accelleration G loads are peak when the bore velocity is peak. Bore pressure v/s bullet position in bore charts show this clearly, the peak pressure point will of course vary based on the burn rate of the propellent, etc. But pressure does not drop to zero until the bullet is long gone from the bore. Until that occurs there will be thrust rearwards which is part of felt recoil.
However, we do generally agree, and I do see your point. It's all about time. But before we go there, consider this:
The recoil pulse is present (albeit variable) until bore pressure drops to zero, which is sometime after the bullet exits the bore.
Even after the bullet reaches it's external ballistics phase, gas is being ejected from the bore until bore pressure drops to zero. This takes a discrete period of time, and during that time you can imagine it as though you are on the receiving end of a low thrust rocket engine (which is exactly what it is at that moment).The time base of the equation is the key... that goes both for the accelleration phase and the decelleration phase. One thing that soft armor does as opposed to hard armor is to lengthen the decelleration phase, thus lowering the peak loads produced. Hard armor deforms less, but the time base for decelleration of the projectile is shorter. The recipient will feel it as a sharper "crack" against the armor as opposed to a longer and softer "thump" with soft armor. Naturally we are talking milliseconds here, but in physics milliseconds are a liftime...
Double the time base and the peak G loads are reduced by a huge amount. Make the time base 10X and the the forces drop off... orders of magnitude and all... and this is what your math shows. S0: A firearm produces X Joules of energy. By definition half is projected in one direction and the other half is projected in the opposite direction. The felt result (at either end) is all based on the mass of the system in motion and the time base over which the force is spread.
Should I run the calculus?
We are getting closer and closer to my professional field of expertise.... More germane to the discussion: The keys to penetration are velocity, sectional density, geometry of the projectile, and projectile hardness. Thin, fast and hard (IE: non expanding)beats the same kinetic energy level delivered thick and slow. Sabot's shedding off of a small diameter hardened penetrator is how it's done on real armor.
Willie
.
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