Hot spent casings

A short course in thermodynamics is in order here by someone more learned than I am but roughly, yes:
heat differential x time x mass x caloric mass = heat transfer

Even though cartridge brass is only .015" or so thick, it still takes time to transfer combustion heat from inside to outside the case.
Think about sweeping your finger though a candle flame. Then multiply the temperature and divide the time.

What caliber or calibers were you firing? What load?

tipoc

I think it's because the cylinder spins so fast. yea!

....best thought we had was the semi ejects at once leaving the casing to cool on it's own while the bolt action was not being ejected for a few seconds allowing the barrel to serve to some degree as a heat sink.

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That's exactly right. A semi extracts and ejects the casing before it can pass the heat through to the chamber walls.

Every metal has a rate of heat transfer. So even though there's a big flash and fireball inside the casing it's gone before much of the heat can pass through the casing and into the walls of hte chamber. Which leaves the exposed barrel bore as the primary heat transfer location in a semi auto. It's also why ejected casings from a semi auto will burn us if they land on the skin while casings from a manually cycled gun can be hand held easily. Even that brief moment it takes to shuck them out means that much or most of the heat held by the brass passes to the gun.

And by the way, you DO realize that you posted a rifle question in the revolver handguns forum, right? You may want to get a moderator to move it for you.

are you comparing the same caliber bolt to semi?

is your semi a gas operated gun blowing back HOT gasses to cycle the action? ie remington r15 or r25

what is the rate of fire in this controlled experiment? I can pump a lot more rounds with a semi auto and heat up the barrel to transfer heat to the brass.

Plus hot brass that finds a gap in your clothes is better than a double shot of espresso!

BCRider answered the question above. Plus brass cools off very quickly.

tipoc

tipoc said:

BCRider answered the question above. Plus brass cools off very quickly.

tipoc

Click to expand...

I guess so, but even several minutes after firing a magazine through my 308 semi auto, when I go to find the empties and pick them up, they are still uncomfortably hot to hold in my hands.

several minutes

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Not to dispute you but usually, unless the hot sun is shining directly on them, 3 minutes is a good piece of time for a .308 case to cool off some.

But folks mileage, sense of time and sensitivity of hands may vary some.

But if you want to conduct a pointless test, time it sometime. How long after ejection and the case hits the ground, before you can comfortably pick the case up. Bolt action vs. semi. Then you'll know beyond dispute and can brag on it some.

tipoc

.best thought we had was the semi ejects at once leaving the casing to cool on it's own while the bolt action
being ejected for a few seconds allowing the barrel to serve to some degree as a heat sink.
That's exactly right. A semi extracts and ejects the casing before it can pass the heat through to the chamber walls. [/HTML]
An auto always ejects hot brass and a manual operated gun always ejects cooler brass. Now for the exception that proves the rule.......
....I have a Remington model 81 in 300 savage.
It gently launches the brass up and half the time they hit my face or the top of my bald head.
but its not a problem because they are barely warm.

The M81 is a "long recoil" action and the case stays in the chamber for maybe a tenth
of a second or so while the barrel travels back out of battery.
Thats all the time it takes to transfer most of the heat energy.

tipoc said:

Not to dispute you but usually, unless the hot sun is shining directly on them, 3 minutes is a good piece of time for a .308 case to cool off some.

But folks mileage, sense of time and sensitivity of hands may vary some.

But if you want to conduct a pointless test, time it sometime. How long after ejection and the case hits the ground, before you can comfortably pick the case up. Bolt action vs. semi. Then you'll know beyond dispute and can brag on it some.

tipoc

Click to expand...

That's a good idea. A pointless test, but one which I will truly enjoy! Stay tuned for more~! Soon as my broken neck and back heal, it is off to the range with a watch, maybe one of those laser thermometers to remove the human subjectivity element...

I believe it's because of that theory that the semi-auto ejects that hot case so fast that it has no time to transfer any of that heat to the walls of the chamber. I used to shoot NRA Hi-Power matches with an M1A back when most of the guns on the firing line were M1A's or M1 Garands. Those cases come out HOT and when a .308 or .30-06 case gets ejected from someone else's gun and hits your neck and gets caught between your neck and the collar of your tee shirt you discover how hot they are when they come sailing out. They do cool off pretty fast though. Can't recall ever getting hit that way with any .223 from an AR and IIRC I only got hit that way once with a .30-06 case but it was one hot case.