Q: Why is the brass so hot?

T

Target Shooter

New member
Why is the brass so hot when it ejects from a semi-auto firearm?
I can fire a round in my bolt gun and eject it as soon as it fires and it seems to be cool within seconds. The same load out of my semi-auto and the brass stays hot for nearly half a minute.
Why is that?

TS
 
A

Art Eatman

Staff in Memoriam
Time. With the bolt gun, the heat transfers to the steel in that longer period of time before ejection.

After maybe ten quick shots from a bolt gun, and the heat has built up, the difference would be notably less.

Art
 
R

Ruben Nasser

New member
Art is right!!

FWIW, the efficiency of guns is only about 1/3, only 33% of the powder energy is tranformed into kinetic energy, almost all the rest is trasformed into heat.
 
A

Archie

New member
Hey TS, are you talking about the same cases?

Is the bolt gun and the semi auto in the same caliber, that is?

A larger piece of metal will hold heat longer than a smaller piece. Also, different metals will hold heat longer than others. (But I can't remember if steel has a faster transfer than brass right now.)

And lastly, the amount of powder burned has something to do with it. Burning 80 grains of powder makes more total energy than burning 3 grains.... no?
 
Q

Quartus

New member
Why is the brass hot?

Why is the BRASS HOT?????


Fer cryin' out loud, what kind of dumb question is that?

Everyone knows why the brass is hot!

It's hot so it can find its way farther down your shirt! If it were just warm, you wouldn't dance around like a fool and give it the chance to work its way down your shorts.


I thought everybody knew that!

:D
 
S

scouter27

New member
A larger piece of metal will hold heat longer than a smaller piece.
Click to expand...

Archie, wouldn't the larger surface area cause it to loose heat faster? That is why they put fluting on some barrels. If the larger case got hoter to begin with, then I understand.

BTW, brass is a better heat conductor than steel.
 
T

teufelmann55

New member
Powder generates two things when it deflagrates:
Heat & Pressure
(I'll use a .308/7.62mm M-14 style rifle as a model)


1 primer detonates
2 powder starts to deflagrate and create pressure
3 when the pressure overcomes the pull weight of the bullet (around 60#) it pushes the bullet out of the case into free flight (the zone before the bullet contacts the rifling).
4 Bullet engages rifling creating a gas seal
5 Case obturates to create a gas seal-great heat and pressure by this point
5 as powder burns away and the bullet gets further down the barrel the pressure subsides a bit allowing the case to cool and shrink away from the chamber walls.

At the point of extraction at least on a semi the case is just cool enough to be extracted-usually taking about 1/12th a second or so from primer detonation to extraction
In the 14/10,000 of a second from primer detonation to the bullet exiting the barrel over 4000 horse power have been generated to propel the 147 gn. bullet over twice the speed of sound. That is alot of heat and pressure in a very short time coupled with the short time to extract leaves not alot of time to transfer heat away from the brass.

Hope that clears up things for you abit
 
T

Target Shooter

New member
Thanks for all the answers guys...Actually I wasn't searching for an answer although I did write it that way. Just wanted to see what kind of responses I would get. (Already knew the answer)
Very good answers and the hysterically funny one from the captain.

Yesterday I was out shooting with "Phil in Seattle" and I had a screen up to my right so I don't spit hot brass on the other shooters. Well while shooting my Garand one piece ejected from the rifle, flew up and hit the screen and landed on my arm. HOT!...HOT!...
Well I was in a good hold but I had to lift my head and arm and wipe the hot brass away. Went back to my stock weld and the damn case rolled back down the shooting bench from the next round I fired and laid against my other arm...STILL HOT!:mad:

So that's why I was asking..."Why is the brass so hot when it ejects from a semi-auto firearm?" I guess more of a complaint?

Thanks,
TS
 
G

GLJones

New member
Refrigeration

This is why I store all my handgun ammo in the freezer.

The powder can only inject a finite amount of heat energy into the brass cartridge. Start with a lower temp and the heating cannot make them as hot.

If you reload, try putting a drop of "Blue Ice" with your powder.(buy the Blue Ice at Walmart and open the container to get the blus liquid) Freeze overnight and in the morning you can shoot.

One of three things will occur:

1) Brass will be cool to the touch when it hits you.

2) Gun will explode sending shrapnel into you and your shooting buddies.

3) Nothing. Powder refuses to ignite.

Best thing to do, wear a cap with a bill and long sleaves.
 
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