Barrel extension material failure?

[Xferbuckeye]

Anyone seen something like this and is it anything to worry about? I scrubbed the carbon from the chamber and extension in an AR10 to find some spider webs in the extension material. They are enough to catch a brass pick on. The gun has a 10oz heavy buffer and is shot suppressed with the gas turned down.

Pic is tough to get but did my best. The best example I could come up with for a description otherwise is if anyone has an older stainless knife and it gets the black spider web cracks in it. The cracks are all by the ejector opening.

Appreciate anyone’s $0.02

 

[bfoosh006]

How many rounds thorough it ?

I don't know if those would concern me much. it kinda looks un-finished, or not fully polished ?

However... in the pic, the marks at the bottom middle of the feed ramps ? Is it just the lighting or are the rounds tips smacking that ?

 

[Xferbuckeye]

It was polished when new. Has 1500 rounds on the gun and barrel. The gun is a Larue OBR and sat in the safe for a few years before I got it back out two years ago.

The idiot marks are from me prying the bolt back to eject a series of rounds that stuck on me last hunting season. The marks on the extension are from a year later. Rounds don’t touch that area but it sure looks gnarly!

 

[papershredder]

Throwing out a couple ideas here and even more questions, more detail will be helpful. It kind of looks like fire cracking. Running gas tuned down, the bolt shouldn't be unlocking too early, but maybe the extra heavy buffer is too heavy and your gas setting may still be higher than necessary compared to using standard H2 or H3 buffers? The carrier shouldn't move until the bolt completely unlocks. Is recoil heavy or is it light but bolt travel seems slow/sluggish? Maybe your chamber is too large and your getting excessive gas blowing back past the brass into the chamber and receiver before bolt unlock? Have you fired it in low light or at night, and if so, is there a flash coming out of the ejection port? Those rounds that got stuck, were they handloads or factory? If handloads, post pictures of some fired brass. How does your fired brass compare in size to new brass? Is your brass covered in soot after being ejected?

With all that in consideration, 1500 rounds so far and for the most part running fine, I wouldn't be too concerned. There doesn't seem to be any burrs or wear on the extension lugs; so I assume the bolt lugs are in similar condition, correct? Make it a point to periodically inspect the bolt assembly and the cam pin for signs of excessive wear.

 

[Xferbuckeye]

Fire cracking is exactly what it looks like and that’s the best description it could have to explain the shape and texture.
Rounds are always covered in soot. Gas gun and suppressor filthy and then some. On many rounds you can see the outline of the grooves that Larue puts in their chambers. The stuck rounds were hand loads but FL sized with a bushing (Redding). Every few would stick to the point the only way they were coming out was with a screwdriver and some elbow grease. Went to a Forster FL die and haven’t had that problem since. Still filthy though.
Bolt looks fine, cam has the finish starting to wear but normal. I clean it every time I shoot it bc it gets so fouled.

I’ll get a couple more pics but Larue told me to shoot it after not listening or looking at the pics I sent them. And shoot it near dark is a good idea. More to come and thanks for the input.