My Colt upper does not have this problem, but I have read enough about it to be curious. How often is this a problem with a factory taper pinned FSB? I bought mine very lightly used, and it does have a bit of rust colored “stuff” coming out from under the FSB on both “legs,” which I was not really concerned with. However when I started reading about it, I began wondering what might cause this on an otherwise factory standard gun. I get the impression that this is a fairly rare problem. My upper is genuine Colt, and I know it is parked under the FSB, so I also wonder where the light brown/red discoloration is coming from. No malfunctions with this gun by the way.
normal, not a problem. blast it with lube from time to time.
What brand is the barrel? I had an LMT upper that looked liked the FSB took a bath in salt water the first time I shot it.
It’s Colt, the entire upper save the BCG is Colt. The BCG is BCM. Do you have any functioning problems with yours? Mine if far less noticeable than yours.
It’s fine man. Perfectly normal. In fact it’s one of the inspection points I used back in the day when I was a hard charging NCO. As long as the gun runs, your fine. The chances of a factory colt barrel being jacked in very low.
Thanks bro. I guessed as much, and like I said, I just got curious about it after reading some other threads on the subject.
This only happened the first time I took it out. I read somewhere that it was from chemicals left over from Parkerizing burning off.
I wouldn’t worry about that.
I had a leaky FSB on a new upper that had to go back to the factory. It looked way worse than any pics I’ve ever seen of people’s soot smudges and whatnot, and it shot sparks out when you fired the weapon. If it was an issue, I would think that it would be obvious.
Another one of LMT’s corner cuts. As we learned from Randall @ AR15barrels.com, the FSB should be taper pinned to the barrel because the taper pins actually help pull the FSB down onto the gas port. Thus a properly taper pinned FSB will hold a better gas seal all things equal.
I have noticed it on several of my rifles, they still function though. I put together a $169 DD barrel with a Y/M low profile gas block and it leaks. It was a barrel I received with the gas port at ~.050 I had to drill it out to .068 before I got reliable function. The leak was not a big one, but I factored it in anyways.
I checked it by blowing cigar smoke into the barrel while I had it and the gas tube plugged from the chamber end. I noticed a bit of smoke coming out around the gas tube going into the gas block as well.