spent case temperature difference

Another point, for those who remember their school science, pressure IS heat! And, heat is pressure.

Note that the hottest rounds coming out of semi autos are also the highest pressures. Rounds from blow back guns are hot, but not burning hot. Move up to 35k psi like hot 9mm and its a different matter. Move up to the 55k psi rifle rounds and they are hotter yet.

No doubt other factors play their parts, but don't overlook pressure, AND, its duration as a factor.
 
Your point on pressure even brings up the point that the brass balloons when fired, there's a bit of friction as the bullet is pushed out of the brass and then some drag when it's pulled out.

The actual amount of heat in calories that a piece of brass actually absorbs, or whatever unit we would use for it, has got to be really small. You could heat pistol brass up with a stick match.
 
Maybe it's even simpler. Whatever isn't turned into the kinetic energy is going to be heat. Now all we need to do is determine exactly how much chemical potential energy there was in the charge, subtract energy at the muzzle, collect and measure the energy that a.escapes with the flash, account for the energy lost to bore friction, and we will be left with a truly useless number that will not even remotely come close to what heat remained in the chamber.

My wife tends to ask me "science" stuff, and Lord almighty, it's hard to tell her that even "science" has limitations. Of course we know what the moon weighs. The astronauts weighed it back in the sixties.
 
I wish I had the technical expertise you guys had, what math skills I had drained out on a stainless steel table a while back. Monday I was trying to do a simple thing, stupid simple. Convert a measurement taken in 1/100 inch into 1/64 inch. I'm sure that I could have figured it out if I put it on pAper, but by the time I gave up, my head hurt.
 
Maybe it's even simpler. Whatever isn't turned into the kinetic energy is going to be heat. Now all we need to do is determine exactly how much chemical potential energy there was in the charge, subtract energy at the muzzle, collect and measure the energy that a.escapes with the flash, account for the energy lost to bore friction, and we will be left with a truly useless number that will not even remotely come close to what heat remained in the chamber.

My wife tends to ask me "science" stuff, and Lord almighty, it's hard to tell her that even "science" has limitations. Of course we know what the moon weighs. The astronauts weighed it back in the sixties.
Click to expand...
:D:D:D:D:D:DPost of the month contender.
 
" I know the AR sends gas back into the receiver--but I still don't see how that can account for such a marked difference. "

I don't think you can use that idea. While doing a preliminary zero on my new piston AR(no gas in the action), I grabbed a case that missed the brass catcher and was rolling off the bench. It was every bit as hot as the one fired by the DI AR I'd just fired that bounced off the spotting scope and landed on my hand.
 
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