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# When is barrel too hot?

Discussion in 'Black Rifle Forum' started by biscotrip, Nov 7, 2012.

1. ### biscotrip

260
0
Mar 7, 2011
Not sure if this is a dumb question, but. How can you tell if your barrel is too hot and you should stop shooting? I have the Smith & Wesson MP15 Sport

Last edited: Nov 7, 2012
2. ### TucsonGlockerYoung Gun

132
0
Mar 21, 2011
AZ

[ame]http://youtu.be/Kzfm4pYhIyY?t=2m36s[/ame]

(Honestly I'm too new to the AR platform to give you a legitimate response, but I thought this would entertain you until someone more knowledgable came along)

3. ### mjkeat

Jun 17, 2009
Midwest
When the steel become plyable. lol

4. ### bigmoney890

Nov 8, 2011
Boone, NC
Honestly, you'll probably never reach that point unless you are purposely trying to get the gun as hot as possible.

1,951
83
Jan 31, 2011
Las Vegas, NV
That's a good question. A gun is roughly comparable with a combustion engine, such as car gas/Otto engines, Diesel engines and aircraft turbines. They all work after the same princibles and all burn carbon to function. All produce about the same exhaust gas temperatures, also known as, Stoichiometic gas temperature.

Stoichiometic gas temperature just means it's the actual gas and/or flame temperature and not the temperature of the surrounding metal/matter in which hot gases flow through, exhaust gas outlet valves in a car engine for examble.

The exhaust gas temps of a car piston gas engine are about 600-850 degrees Celsius (I am too lazy to convert to F)

Of a Diesel piston engine about 800-1050 deg.

Aircraft turbine exhaust gas temps (EGT) are similar to a Diesel piston engine.

The surrounding metal, chamber and barrel in our case stays automatic cooler than the EGT, because hot gas is a weak heat/kinetic energie transferor to matter with greater mass. How much coller the surrounding metal is is hard too tell right out, because it needs to measured or calculated. But one can say it stays roughly about 50-60% cooler than the EGT under full load.

So our barrel temperature probably reaches about 350-430 deg. Celsius (which is absolutely fine with a modern barrel and without plastic hand guards) under hours of full auto, which I believe can not get much hotter, because the fire rate of a full auto rifle is not high enough to burn enough carbon which would produce more energy in form of heat. Also, carbon is a relatively low energie storage. Its energy output is limited. A nuclear reaction is a much better... you know. EDIT: A car engine would over heat to a certain temp and then stop when the heat output of the gasoline is exhausted, if you drain the coolant. It doesn't over heat necessarily because of the metal expansion, it's more because of the braking oil film on the bearings and piston rings.

I believe the barrel doesn't mind 800 celsius, but I am sure it can harm other rifle parts like the gas tube, handguars, and other parts, Ohh and the round might go off if you would chamber one into a 800 C chamber. The question is what happens with the barrel if you fire a round through it, will it lose it's straightness due to more barrel flexing when it's extremley hot? I don't know. It needs to be tested. Again, I just made rough estimations here, everything needs to be tested to make sure.

Last edited: Nov 7, 2012

12,924
60
Oct 8, 2001
Middle of SC
I've seen a 240G heat up so hot, the barrel was glowing red and lobbing rounds about 30 feet.

That's too hot.

7. ### M&P15TBeard One

22,738
4,795
Apr 7, 2011
Arlington, VA.
On a related topic;

There's nothing like the first few mags through a new rifle, that smell of whatever it is burning off.

They oughtta make an air-freshener that smells like that, so you could hang it off your rear-view mirror.

8. ### TangoFoxtrotOIF 04-05

4,272
80
Sep 10, 2008
Nowhereville, USA

When the barrel is cherry red in low light.

9. ### K. Foster

2,601
509
Feb 19, 2002
Mo.
In semi auto, it&#8217;s not an issue. I've gotten my LMT smoking hot several times. Doesn't hurt anything, as long as you don't touch the barrel.

10. ### fnfalmanChicks Dig It

51,471
3,831
Oct 23, 2000
California & New Mexico, US
When the plastic handguard starts to melt?

11. ### JBG30

825
5
Apr 16, 2001
Pittsburgh, PA
Watch the video at 2:08. Can someone tell me what happened at 2:14???

The magazine is removed, the charging handle pulled and a (casing?) is ejected, the gun then fires with no hand on the trigger?

Last edited: Nov 9, 2012
12. ### M&P15TBeard One

22,738
4,795
Apr 7, 2011
Arlington, VA.
The chamber is so hot it fired the round...maybe....probably.

13. ### M&P15TBeard One

22,738
4,795
Apr 7, 2011
Arlington, VA.
OP, especially when new, your barrel will smoke and give off a nice aroma. That's just stuff from the manufacturing process burning off, don't fear it.

14. ### Armchair CommandoLong Range Guru

Jan 10, 2006
Bunker in the Midwest
Unless your running full auto it most likely won't be a problem.

posted using Outdoor Hub Campfire

15. ### Matthew CourtneyInstructor #298

Oct 14, 2002
Lake Charles
The smokeless powder used in modern small arms ignites at between 275 and 400 degrees fahrenheit. Leaving a round chambered in a barrel which is over these temperatures can cause the rifle to fire without the trigger being pulled. This is commonly refered to as "cook-off". It can happen as quickly as 10 seconds in an extremely hot barrel, or ten minutes later in a moderately hot barrel.

Accuracy may degrade with a hot barrel. POI definately shifts as a barrel heats and cools. Hot barrels likely wear out more quickly, although this has not been evaluated in depth with modern melonite treated barrels.....

Last edited: Nov 10, 2012
16. ### Cole125Silver Member

Apr 5, 2008
Far West, USA
It depends on the barrel and the material it is made out of.

The directions that came with my Noveske recon stainless barrel say "if you shoot it hot enough to brand cattle with it will decrease accuracy".