Gas to Bolt brass temp?

[donho00]

I recently had my gas and bolt 260rem out.

I switched back and forth. This range required you to pick up all your brass.
and I noticed something odd.

my bolt gun, I would eject slowly so the brass would just drop out. I would pick it up right away
and stick it back in the plastic tray. Brass would be warm

The Gas gun. I would shoot a 5 round string. Then go walk around picking up brass.
Even with the extra time. The brass was very hot.

I dont see any cratering or overpressure signs. and its all factory ammo
It is not a tight chamber. No issues ejecting or feeding

Why the drastic temp difference?

 

[Snuby642]

Wag.

The brass in the bolt gun, it's like a heat sink till extracted.
Brass comes out gas gun immediately, retaining heat.

 

[donho00]

But I have fired a shot on my bolt. ejected immediately. and picked it up from the bench/ground and placed it in the tray
It is usually just warm. The gas gun brass sits for maybe a minute or two and they are still very hot.

 

[Snuby642]

Was just a guess.
The bleed off of heat or cold into a metal conductor is more rapid than air I belive.

 

[b6graham]

not just your gun that does it. common with gas guns. scorching hot.

 

[donho00]

That would make total sense. If i took my time and ejected the bolt gun. But even if I do it immediately.
Its easy to grab. The gas gun are burn your fingers hot, even after much more time

 

[Snuby642]

I have never taken a temperature from a fresh ar round. I do know if trapped inside a shirt till cooled the brand will last for a while.

Makes it hard to maintain trigger press.

 

[donho00]

I have done the hot brass dance many times!!! Especially indoor ranges

 

[Precision Underground]

Its because it’s being pulled from the chamber so quickly. Most people say that’s because there is no time for the heat to transfer to the chamber from the brass but I would say it’s more likely a product of friction between the case and the chamber as it’s ripped out a fraction of a second after expanding. I can run the bolt on a gun 1/2 a second after firing and the case is cool. There is no possible way that much heat is transferring from the case to the chamber in 1/2 of a second.

 

[Snuby642]

Thats plausible.

 

[Snuby642]

Next time you get a hot round down the shirt, try making the shot without disengaging. It can be done.

It's not a macho thing it's a concentration thing.

If you still hit the mark your wired tight.

 

[donho00]

Its because it’s being pulled from the chamber so quickly. Most people say that’s because there is no time for the heat to transfer to the chamber from the brass but I would say it’s more likely a product of friction between the case and the chamber as it’s ripped out a fraction of a second after expanding. I can run the bolt on a gun 1/2 a second after firing and the case is cool. There is no possible way that much heat is transferring from the case to the chamber in 1/2 of a second.

You think that split second of friction is enough to make it that hot? Just seems like its not a high friction point.
or the ejection would be compromised?? I can rip the bolt back on the bolt even very fast and it is never more then warm

 

[FCS]

Gas gun extracts under pressure. Meaning as you extract the brass from chamber the seal is broken between brass & chamber, hot gas flowing back over case as pressure in bore is not back down to atmosphere.
1) reduces thermal transfer to chamber from brass
2) gets blast of hot gas all along body during extraction.

Watch some high speed video of AR cycling.

 

[donho00]

Gas gun extracts under pressure. Meaning as you extract the brass from chamber the seal is broken between brass & chamber, hot gas flowing back over case as pressure in bore is not back down to atmosphere.
1) reduces thermal transfer to chamber from brass
2) gets blast of hot gas all along body during extraction.

Watch some high speed video of AR cycling.

This makes sense.
OK, so if I turned off the gas. and not let the BCG cycle.
and ejected the round manually, it would be only as warm as the bolt?

 

[Snuby642]

Please try that.

 

[donho00]

Please try that.

actually I just realized that this setup is a dracos barrel. It doesnt have an adjustable GB.
But I will try it with my precision 223 gas gun.

 

[FCS]

Best way to do that is slide gas block forward 0.125” to occlude port.
Even turned “off” most adj gas blocks will still move BCG rearward and corrupt test you are attempting.

 

[longgunJR]

Gas gun operates by redirecting pressured hot gas through the gas block into the gas tube back to the bolt, that heat gets transferred to the brass. Bolt gun is cycled mechanical and so none of that head comes back to the chamber or the brass.

 

[hlee]

Yes, if you turn your gas gun into a bolt gun, the brass will only be as warm as that ejecting from a bolt gun.

I suspect th difference between the two if a function of several factors.

The barrel IS a heat sink, and “immediate” is a relative term. A gas gun ejects the case before you can disengage from the trigger. Steel and brass are both very good conductors of heat and you don’t need much time to get either hot.

A gas gun IS extracting the case under pressure. This means that the case walls are/could be objurated against the chamber walls during extraction. This is not the case in a bolt gun, no matter how quickly you run the bolt. That would cause a lot of friction imparting a lot of heat into the brass.

And, as th gun is extracting brass under pressure, there is some amount of very hot gas that is washing back over the brassas it is being pulled out of the action.

One or more of these may be bigger players than others, but I think that all are in play.

As a an aside, I have a g17 and my sister has a g26. The slide speed is much faster on the smaller gun, and the brass is ejected with substantially more force from the smaller gun. Someone can stand to the side of my pistol and catch the brass as it is being ejected. The brass is hot and you want to put it down. If you try the same feat with the g26, you are looking for immediate burns. The brass is WAY HOTTER when it leaves the gun.

As an other aside, I can feel a noticeable warming to brass when they are being sized in my reloading dies. Yes, that’s a lot of friction, but it is a slow process.

Finally, run a knuckle across a martial arts mat rapidly and with some force and tell me you cannot develop a blister inducing amount of heat from a relatively small amount of friction.

What is find most surprising is that someone didn’t know that semi autos eject HOT brass...

 

[donho00]

Gas gun operates by redirecting pressured hot gas through the gas block into the gas tube back to the bolt, that heat gets transferred to the brass. Bolt gun is cycled mechanical and so none of that head comes back to the chamber or the brass.

so would a piston gas gun not have the same heat transfer?

 

[donho00]

Yes, if you turn your gas gun into a bolt gun, the brass will only be as warm as that ejecting from a bolt gun.

I suspect th difference between the two if a function of several factors.

The barrel IS a heat sink, and “immediate” is a relative term. A gas gun ejects the case before you can disengage from the trigger. Steel and brass are both very good conductors of heat and you don’t need much time to get either hot.

A gas gun IS extracting the case under pressure. This means that the case walls are/could be objurated against the chamber walls during extraction. This is not the case in a bolt gun, no matter how quickly you run the bolt. That would cause a lot of friction imparting a lot of heat into the brass.

And, as th gun is extracting brass under pressure, there is some amount of very hot gas that is washing back over the brassas it is being pulled out of the action.

One or more of these may be bigger players than others, but I think that all are in play.

As a an aside, I have a g17 and my sister has a g26. The slide speed is much faster on the smaller gun, and the brass is ejected with substantially more force from the smaller gun. Someone can stand to the side of my pistol and catch the brass as it is being ejected. The brass is hot and you want to put it down. If you try the same feat with the g26, you are looking for immediate burns. The brass is WAY HOTTER when it leaves the gun.

As an other aside, I can feel a noticeable warming to brass when they are being sized in my reloading dies. Yes, that’s a lot of friction, but it is a slow process.

Finally, run a knuckle across a martial arts mat rapidly and with some force and tell me you cannot develop a blister inducing amount of heat from a relatively small amount of friction.

What is find most surprising is that someone didn’t know that semi autos eject HOT brass...

Of course I knew it ejected hot brass.LOL I learned many years ago, the first time a piece of brass fell down my shirt
But I didnt know why a gas gun brass was SO much hotter then a bolt.

 

[longgunJR]

so would a piston gas gun not have the same heat transfer?

I think it'd be alot less but most likely still not as cool as a bolt gun.

 

[FCS]

Essentially zero difference in ejected brass temp between DI & piston, bore dumps a lot more gas back into chamber than does gas tube.

 

[donho00]

Thanks for the replies
What a great forum. a wealth of info in here

Thanks again

 

[JMGlasgow]

My M14's eject brass that is blistering hot as well, and it's a piston system.

 

[supercorndogs]

My M14's eject brass that is blistering hot as well, and it's a piston system.

Rimfire brass is the same. I think the simple answer is probably the best. Metal heat sinks work well. A semi auto pulls the brass away from the heat sink faster than we can with a bolt action.

 

[Rocketvapor]

No-Gas 22N AR shooter here. (no port, no gas block)
Nice cool pick it up brass.

 

[Precision Underground]

Run some new brass through an expander mandrel very quickly/forcefully and then feel the case mouth when you pull it out. You will see how quickly friction can make brass hot. Multiply that by 100 for it being ripped from the chamber under pressure and it will make sense why it hurts so bad to get one down the back of the shirt! It takes a long time for hot air/gas/flame to transfer to metal. Friction heats it instantly.