Differences in brass temperatures in different rifles

[Lucky6547]

Hello,
I've noticed something odd about the temperature of the brass that's just been fired out of a Winchester Model 70 and an AR-10 style rifle. With the same powder, Varget, the brass is so hot it will brand you coming out of the AR-10 with around 41-42gr; yet with 44.5gr in the bolt gun, the brass is only very slightly warm to the touch. What accounts for this difference? Does the AR pull the brass out so quickly that it is still hot? Does the time it takes for me to lift the bolt and extract the case give it time to pass the heat on to the chamber? But then even in 22 shot strings of fire, the cases don't get warmer over the course of the string of fire when I shoot the bolt gun...and the first and last cases of the AR are always hot...
Just curious as to what would make such a difference...
Thanks,
Ken

 

[LHSmith]

Gas assist....hot gasses are sent back to the action in an AR.

 

[Lucky6547]

Thanks for the reply,
But doesn't the gas just go to the top of the bolt carrier, and not to the chamber? How can it hear the brass from that far away?
Thanks again,
Ken

 

[Lucky6547]

Heat, not hear...

 

[spclark]

Think about it a moment - gas guns invariably extract & eject spent cases sooner than bolt rifles. I'm allowing of course for bolt gun shooters in rapid-fire strings in competition, not what I'm getting at.

Ask someone sitting to the right of an M1A shooter during a rapid-fire stage who's uninformed enough to come to the line NOT wearing a sweatshirt and long pants!

 

[Turbulent Turtle]

It has to do with how quickly the fired case is extracted from the chamber. In a semi-auto like the AR-15 a great deal of heat is removed from the chamber because it leaves with the fired case before the latter has had time to transfer it to the walls of the chamber.

In a bolt action rifle, regardless of how quickly you can manipulate the bolt, the fired case is able to transfer most, or a majority of its heat to the chamber.

The gases that come back to cycle the action in an AR, do so via the gas tube and do not get anywhere near the chamber of the case, they are vented though the BCG key onto the tail-end of the bolt where the rings are.

Handguns have the same issue; cases from an autoloader will burn you, yet you can pick out the fired cases from a revolver with your fingers or dump them in your hand.

 

[dmoran]

The spent case left in the bolt chamber has the barrel steel acting as an immediate heat-sink.
Where as a semi-auto is ejecting the brass within milliseconds of the combustion cycle.