sig 556 the beast!

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[thetaxman]

No issue as far as I know.

It is a Sig so no need to overclean it!! Mine is at 11,500rounds and I run a bore snake through every few thousand rounds and keep it running fairly wet. Never had an issue.

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[7.62 Charlie]

Did you try to clean it off? It might just be gun powder.

[$P-Ritch$]

It sounds like its where the port for venting the excess gas out of the gas tube is. After a while it'll cake up some carbon on the barrel. You can keep cleaning it off, but there really is no need. It is just the way the gun operates and it's completely superficial.

Sounds like your sig556 is running like a champ. If ain't broke, why fix it (for cosmetic concerns)?

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jgjj

[SJgunguy24]

It's fine, just imagine what the bolt carrier of a DI AR goes through when all of that gas gets blown back into the upper reciever.

Good to hear you clean your guns......that Saiga you sent me was fricken nasty.

[IsaacGlass]

What ammo brand?

[captbilly]

It sounds like its where the port for venting the excess gas out of the gas tube is. After a while it'll cake up some carbon on the barrel. You can keep cleaning it off, but there really is no need. It is just the way the gun operates and it's completely superficial.

Sounds like your sig556 is running like a champ. If ain't broke, why fix it (for cosmetic concerns)?

I don't know of anyplace on an AR that vents off excess gas out of the gas tube. Could you please describe where this is?

It is my understanding that the gas from the gas tube goes to the bolt carrier and is used to cycle the bolt carrier. As I understand it, any "excess" simply ends up in the upper receiver and exits out the ejection port (or sometimes in the face of the shooter if the gas rings are worn).

My guess would be that the OP is seeing the powder residue where some gas leaked out of the gas block at the gas block barrel interface. This is quite common on ARs because the gas block just slips over the barrel (held in place with a pin) and has no way of actually tightening to seal the gases in. Some ARs leak less than others because the gas block happens to be a bit tighter, but only a few gas blocks actually have a good way of applying a significant sealing force against the barrel (set screws so something but not much). I have a JP adjustable gas block that actually clamps around the barrel and may be able to truly seal against an otherwise loosely fitting barrel. (I haven't tried it out yet so I don't really know if it works but it looks like it would.