Unusual "Copper" fouling on Bolt Tail = LiL Gun??????

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Chuck R.

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Not sure where this belongs...

I'm having an issue with heavy "copper-like" fouling on nitrided bolts in a 9" 300AAC build:

1Kccd5J.jpg

Picture is of a relatively new Tollcraft nitrided bolt. Contacted Toolcraft and they replaced it without an issue. Dropped in he replacement and withing 60rds the same buildup appeared. Sent them back the BCG this time. In the meanwhile I dropped in another spare nitrided BCG I bought from PSA, fired 60 rds and the same fouling reappeared. So that's 3 bolts, 2 of which were brand new.

The only possible cause I can think of is it's caused by lil Gun powder I've been using. Previously I was loading with H110 and had zero issues.

I've read some mention of copper fouling on bolt tails & Lil Gun on the Blackout board, but have yet to see a positive correlation. Any ideas???

Thanks,

Chuck
 
Lil gun & H110 have a decoppering agent in it, Tin Dioxide.

I wonder if excess copper is being removed from the bullet on firing? Rough throat/leade?

The gas system may blow copper residue back into the action, when the tin dioxide removes the copper?

But this makes no sense as the 2 powders are in the same family and the burn rate chart has them next to each other?

Is the H110 an old lot that may not have the tin dioxide?

Not much help.

Added more https://www.ar15.com/forums/ar-15/andamp_gt_300_BLK_copper_build_up_on_bolt_tail/118-672749/
A burr in the gas port hole in the barrel is most likely raking off bullet jacket material as the bullet passes the port. It is getting blown back into the bolt through the gas tube and accumulating in the bolt / carrier assembly. The burr will eventually wear off and you should not see this condition persist
 
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Lil-Gun has a high nitro content and runs extremely HOT. This is the reason it's not recommended in revolvers but is normally considered safe for rifles. With Lil-gun its reported that you can burn your self from touching the barrel after very few rounds, it runs that hot. Go back to H110/W296 and the problem will/should go away.
 
Comparing Lil Gun and H110 with 3 different bullet weights show about the same velocity, pressure and weight of powder charge. Hodgdon Data.

Chuck R. What is the loads used? Exact same components , except fot the powder? Case mouths chamfered and deburred??

Suppressor in use?
 
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That sure looks like copper. You could prove it with a swab of your favorite copper-remover bore cleaner.

And with that in mind, if Lil'Gun is that hot (enough to carry copper vapor back to the bolt) I wonder what your gas tube, block, and port look like. Can't be good.
 
The decoppering agent, Tin Dioxide , removes the copper fouling and blows it out the barrel.

Some is going to come back the gas tube, into bolt. Even more so with a suppressor.

The mystery to me is, why 1 powder and not the other? More Nitro in Lil Gun? May melt more airborne copper particals, that are shaved from the bullets on firing?

High heat would advance throat/leade erosion faster.

I would clean the gun and forget about it, as long as it doesn't effect function....
 
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Comparing Lil Gun and H110 with 3 different bullet weights show about the same velocity, pressure and weight of powder charge. Hodgdon Data.

Chuck R. What is the loads used? Exact same components , except fot the powder? Case mouths chamfered and deburred??

Suppressor in use?

No suppressor, same exact components, except for powder. Brass was chamfered and deburred, In addition I put 60 rds of factory Nosler through it without an issue. The only variable is the LiL Gun powder.

I'm going to soak the bolt to get the copper off and check out the rest of the gas system to see if it's building up elsewhere. Unfortunately I've got 8 pounds of LiL Gun and really no other use for it. I may just try to sell it to one of the skeet guys on post and just stick with H110, but then again my H110 is an older lot, probably pre-copper reducing.
 
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