Fire Cracking and Barrel Heat

[centershot]

Went to the range today equipped with my new laser thermometer. Found out that the barrel temperature half way down the barrel was 20 degrees hotter then at the chamber. Why then does fire cracking appear at the chamber?

 

[JMayo]

That is where the explosion is it's biggest ...

 

[Bill Norris]

That is where the explosion is it's biggest ...

Yea, the highest temps are at the chamber area at time of ignition. It probably does cool faster than down the barrel a ways due to the opening at the chamber area as cooler air can enter quicker.

 

[Multiracer]

That is where the explosion is it's biggest ...

...and midway down the barrel the friction is greatest.

 

[Dkk37058]

If you have a contoured barrel it’s thinner at the halfway point and thickest at the chamber area
That’s my 2 cents worth of information

 

[Dgd6mm]

All the above.

 

[YEW PLUCKER]

A follow up question > when a barrel fire cracks it is said to be hard on reamers to re chamber or set back, so without assuming can some one explain just what’s going on that increases the level of difficulty and is the barrel now hardened like heat treating a tool ?

Dumb question I know..

You're tempering the steel. It cracks because it has lost all of it elasticity, hence cracking. Eventually it will be as hard as the reamer.

 

[DaveTooley]

You're tempering the steel. It cracks because it has lost all of it elasticity, hence cracking. Eventually it will be as hard as the reamer.

E
Tempering is used to reduce the hardness of the steel. 416SS will only get to about Rc 40. 28-32 is the range of the steel when a barrel is made. Heat checking is impregnated with carbon from powder residue. Carbon is hard and shortens the life span of the throat area.

 

[DaveTooley]

If you're doing the work then maybe. If you have to pay someone then I wouldn't do it.

 

[jelenko]

@DaveTooley
This barrel only has 1142 rounds, I was thinking about a set back although I’m not sure if it would be a good candidate or if it’s too far gone.

Hmmm. The lands look smooth. The stuff in the grooves - is it carbon?
My lands show cracking before the grooves.

 

[TTE]

Heat Relief -

https://www.harborfreight.com/20v-cordless-high-volume-inflatordeflator-tool-only-57166.html

 

[6.5 forever]

Heat Relief -

https://www.harborfreight.com/20v-cordless-high-volume-inflatordeflator-tool-only-57166.html

Have tried this as a barrel cooler?

 

[DaveTooley]

Pic #1&2 are the top of the lands. Lands make 100% contact with the bullet and have the highest barrel to bullet pressure. Thus higher temperatures. Thus heat checking.

 

[TTE]

Have tried this as a barrel cooler?

Yes. Put on some vinyl tubing and stick it in the chamber. Trigger is on/off (don't have to hold it on), moves a lot of air (24 CFM) and with the extended battery lasts 3 hours of run time. I like mine !

 

[Shooter13]

Heres the deal for me and I'm not a @DaveTooley as I'm sure he had forgotten more than I'll ever know about this stuff, the 3rd picture of the chamber end doesn't look bad to me at all! What is the target telling you? I have barrels that shoot great and look far worse than that!! Sometimes I think maybe they shouldn't have given shooters a barrel scope

 

[6.5 forever]

The target is why I pulled the barrel, it just was no longer competitive as tuned. So rather than using up more H4895 and primers, I swapped it out for a new barrel that shoots half the size.

Jim

The best thing to do for sure.

 

[Shooter13]

The target is why I pulled the barrel, it just was no longer competitive as tuned. So rather than using up more H4895 and primers, I swapped it out for a new barrel that shoots half the size.

Jim

That sir is exactly why you change barrels!! Good luck with the new one!

 

[DaveTooley]

We all have reasons for retiring a barrel, or not. On my 1K BR rifles I would retire them every two years. I didn't want one to lay down on me just before the Nationals. If it's a rifle you use a lot . Plan ahead

 

[Webster]

A follow up question > when a barrel fire cracks it is said to be hard on reamers to re chamber or set back, so without assuming can some one explain just what’s going on that increases the level of difficulty and is the barrel now hardened like heat treating a tool ?

Dumb question I know..

I wish I still had an article probably published by the military. It explained the chemical and phase changes that occur at a very shallow depth at the surface. The analysis was just on carbon steel barrels. Most of use have SS barrels. You cannot temper most types of stainless steel. I will look for the article. There's no reason to really be concerned, it always happens and it's normal. It's actually called hot gas erosion.

https://apps.dtic.mil/sti/pdfs/ADA440938.pdf

52 page miltary research article on erosion. I don't think it gets into sophiticated analysis of chemical and metallurgical changes at the surface, Will look for another article on metallurgical changes.

 

[6.5 forever]

I wish I still had an article probably published by the military. It explained the chemical and phase changes that occur at a very shallow depth at the surface. The analysis was just on carbon steel barrels. Most of use have SS barrels. You cannot temper most types of stainless steel. I will look for the article. There's no reason to really be concerned, it always happens and it's normal. It's actually called hot gas erosion.

https://apps.dtic.mil/sti/pdfs/ADA440938.pdf

52 page miltary research article on erosion. I don't think it gets into sophiticated analysis of chemical and metallurgical changes at the surface, Will look for another article on metallurgical changes.

It's always good to understand what is happening when all you can see is the result.