Rust-colored residue on AR barrel/handguard around gas tube?

[Chris17404]

Hi all,

I was just rearranging the handguard covers on my BCM upper when I happened to notice a rust-colored residue of some sort on the top of the barrel and in/around the cuts in the handguard. This residue only appears on the top of the barrel to the rear of the low-profile gas block and under the gas tube. It does not appear in front of the gas block nor the rear end of the barrel or handguard closer to the receiver. When I rub some off with a Q-tip it appears blackish, but on the barrel and handguard it appears more rusty color. I'm just wondering if there's anything to be concerned about regarding gas escaping improperly, etc. The rifle shoots fine. I wouldn't have noticed anything had I not removed the rail covers. Maybe it's just residue from the gas tube getting hot while shooting, and all is well. That's likely it, but just wanted to check. I can upload pics if you like, but I think I described the situation pretty well. Thanks for any insights you may have.

P.S. I just cleaned the residue off the barrel and rail with some rubbing alcohol and Q-tips. Going shooting tomorrow and I'll check if there is any additional build-up.

Chris

[ABNAK]

It is gas residue. Maybe your gas tube isn't a tight enough fit and is leaking? It's not uncommon to see a tiny bit right around where the tube goes into the FSB/gas block but if it's all over you likely have a fitment issue with the gas tube.

[Chris17404]

Update: I contacted BCM customer service and described the issue. Based on my description, they said it seemed like carbon build-up and was "completely normal". I asked them where the carbon could be coming from other than the gas block, which isn't good. They said the gas tube can have a very slight gap where carbon deposits can get through and show on the gas tube and barrel. I asked BCM if I could ship the upper to them for inspection. They sent me an RMA number and I shipped it. The armorer inspected it and "to speed up return of the upper to me", they went ahead and replaced the gas block and gas tube, test-fired it, and did not see any residual carbon fouling, and shipped it back to me. Round trip time was 2 weeks. It also appears they completely cleaned the upper and shipped it covered in their preservative. Overall, great customer service. I still have an email out to them asking for more details as to what exactly the armorer may have found wrong with the gas block. I'll let you know if/when they reply. I'll shoot this upper ASAP and see how the carbon looks after a few hundred rounds. I'm pretty confident the issue is resolved.

[grizzlyblake]

I had a brand new BCM lower with a sticky bolt catch. They paid to ship it back, replaced the bolt catch, and had it back to me in a week. Fantastic customer service.

[MistWolf]

I have seen where the "red residue" was from the factory applied preservative getting warm.