Case Failure Not From Overpressure

[mikemo4032]

So, about 10 days ago I posted about an apparent increase in pressure without an increase in velocity in my 6 GT. This was based on how beat up my cases were after firing and a very stiff bolt. I got lots of possible solutions and they were all based on sound reasoning.
Today I went to the range with one more attempt to solve the issue before I pulled the barrel. I immediately got a case failure so I stopped and started taking things apart. I found my Proof barrel had loosened from my Defiance action so much so that I just removed the barrel by hand. I've never known anyone else's barrel to come loose like this. A gunsmith installed this one and I watched him torque to about 75lbs. Could this cause other hidden damage to the receiver. Is this more common than I think?

 

[26Reload]

Not that I like that....but I have been have simular separations lower in case...but with a proof barrel....i will need to check the barrel on the rifle....i am losing several pieces of brass....

 

[243winxb]

Barrels can come loose. A high spot where the barrel makes contact with the receiver is likely. A sign would be shots walking on target as barrel heats up.

Sloppy threads is another.

 

[mikemo4032]

Barrels can come loose. A high spot where the barrel makes contact with the receiver is likely. A sign would be shots walking on target as barrel heats up.

Sloppy threads is another.

Thanks for the info. It really threw me for a loop. It must have come loose towards the end of a prs type match. I couldn't hit targets at 300 yds by the end. I'll reinstall it and see how it shoots.

 

[26Reload]

We're you able yo turn it by hand....
To notice it was loose...

Oops...reread first post....

 

[J E Custom]

The failure area is in the heat effected zone caused during annealing. the added head space allowed the case to expand in the weakest area and it failed.

If you are loading hot loads this can cause case stretch and cases will fail faster. the barrel should never come lose if it is torqued correctly and not over heated.

I would recommend Throwing all of these cases away and start over with proper barrel tightness and head space. back off the pressure, anneal often. and enjoy.

J E CUSTOM

 

[nmbarta]

Glad you didn't get hurt, weird things happen.
I had a 243wssm ar-15 come apart on me a few years ago, accuracy suddenly went in the trash. I didn't think to question the rifle because it shot so well. I thought there was a problem with ammo, it made it about another 15 rounds and then the barrel extension failed and the rifle ended up in lots of pieces (the manufacturer did stand behind it, but informed me that it did not "blow up"). When things change suddenly, it's always good to question everything and make sure it's safe to continue. Most of the "normal" issues don't show up all of the sudden.
It is possible that those loose threads could have compromised the threads on the action, if you don't have the ability to check that out, I would have it looked at. I highly doubt that there was an issue with the action coming from defiance, but your stuck in a spot where it's hard to know what happened. If the machining on both parts are done correctly, and it was properly installed, that wouldn't have happened.

 

[jd5521]

I've seen barrels come loose but only when they were not wet torqued.

 

[bill123]

I've seen barrels come loose but only when they were not wet torqued.

Never mind. I just googled it. Wet torqued?

 

[jd5521]

Never mind. I just googled it. Wet torqued?

Apply moly grease or anther "wet" substance to the threads as to prevent galling and slippage.

 

[bill123]

Apply moly grease or anther "wet" substance to the threads as to prevent galling and slippage.

Thanks. I always do. Just didn't know there was a name for it. Love this site!

 

[mikemo4032]

The failure area is in the heat effected zone caused during annealing. the added head space allowed the case to expand in the weakest area and it failed.

If you are loading hot loads this can cause case stretch and cases will fail faster. the barrel should never come lose if it is torqued correctly and not over heated.

I would recommend Throwing all of these cases away and start over with proper barrel tightness and head space. back off the pressure, anneal often. and enjoy.

J E CUSTOM

Thanks JE Custom and everyone else who has provided insightful input. This web site provides, in my opinion, some of the best advice without all the "attitude" so many others seem to attract. Speaking to a couple of points made; My smith prides himself on cutting threads. I watched him cut, double check the threads and apply lube before he torqued. Not saying there are no issues there, it's just what I observed. To J E's point of hot loads, I would say these are mid level loads pushing a 109 through a 26" barrel at about 2950. Some of my buds push to 3040. It's easy to find the affected cases, they have deep extractor mark's and they are 40 to 60 thousandths longer. I am not kidding.
So thanks to all and I'll post an update when I get it back together.

 

[BallisticsGuy]

So it was caused by headspace suddenly getting big. That's not pressure, that's bad physical dimensions. As far as damage to the receiver, no. Snug the barrel back up and go shoot.

 

[ntsqd]

Torque is a can of worms. The tension in the fastener or compression in the assembly generated by one torque value changes with the type of lubrication used (or not used) in the threads. If the lubrication is listed with the torque spec don't assume that means that any lube will give the same results. If the torque spec is for threads lubricated with 30wt. oil don't think that Lock-tite 271 is going work the same, or that anti-seize will either.