I had a spare complete lower from years ago, so decided to put it to good use and build an upper for it.
Barrel - Blackhole Weaponry 5.56 caliber 20" length, Twist: 1x8, AR15 Gas system: Rifle, Profile: National Match (.750 gas block)
Gas Block - Midwest Industries AR-15 Low Profile Gas Block .750 Black MCTAR-LPG
Gas Tube - CMMG AR-15 Rifle Length Gas Tube Kit Gas Tube/Roll Pin Stainless Steel Silver 55DA196
(there are other parts involved, naturally, but I don't think it's relevant to the question. Happy to expand on it though)
I put ~ 70 rounds through it, making sure it cycles. Sure does.
After about 20 rounds, I noticed some markings on the part of the upper receiver right after the ejection port, right before the forward assist (the little triangle looking part). It looked as if the brass was bouncing off that part. It made it look like it was a little under gassed. But as the buffer spring was for a carbine rifle, I thought it might involve that.
When I went to clean it, I started noticing a bit of carbon around the gas block (see pics). The carbon is enough to come somewhat on top, in front of the gas block, and around the gas tube where it comes in contact with the gas block.
After doing some reading, I saw some suggesting taking the gas block off to check the alignment. Others suggested sealing the gas block with locktite.
I went to take the gas block off to clean it, and it wouldn't budge. I used a rubber mallet, a hammer, a chisel, and nothing. It was going no where. So taking it off to clean it isn't going to work, unless I'm prepared to do serious damage to the barrel.
So, should I be concerned? Should I take it to a gunsmith, or just hope the carbon eventually seals up all the gas leaks?
Gas blocks are not airtight. They WILL show some carbon leakage until the carbon seals it up, some never stop showing new carbon residue.
Brass marks on the side of an upper are normal.
Quit worrying and go practice more, and take a nooby to the range with you to spread the disease.
Then drag them to an Appleseed for more infection :)
The triangle thingy on the upper is actually the brass deflector block, brass is supposed to hit that. A little rubbing with oil or cleaner will take the brass marks right off. If the rifle is running right chances are the gas block and gas port are indeed aligned properly. Most barrels have indents where the gas block screws sit in to. If your block screws are in the indents your good. More than likely if alignment is off, you're bolt won't run back and load another round. As eagle said, most blocks aren't completely air tight......
SK,
The fact that the gas block won't come off would worry me more than the leakage. Since you casually mentioned it, did you put any locktite on it? One thing you can try is to apply heat to the gas block. I use a propane torch and heat the part you want to remove (not the barrel). I then use a piece of hardwood as a punch and slowly push it out pushing from different directions. Liberal applications of Kroil wont hurt either.
aj
Well that makes me feel more comfortable!
airplanejoe - No, I didn't use locktite to put it on. It was a very snug fit to start with, and I had to put some froglube on it and give it some heavy taps with a hammer to get it into place when I installed it. I ended up marking the outside of the barrel a little while installing it. I know I could probably take it off by heating it with a blow torch and tapping it off (at least I hope). But unless I need to, I don't know why I would.
Quote from: Specialkay on September 03, 2016, 09:01:50 PM
Well that makes me feel more comfortable!
airplanejoe - No, I didn't use locktite to put it on. It was a very snug fit to start with, and I had to put some froglube on it and give it some heavy taps with a hammer to get it into place when I installed it. I ended up marking the outside of the barrel a little while installing it. I know I could probably take it off by heating it with a blow torch and tapping it off (at least I hope). But unless I need to, I don't know why I would.
Leave it alone.
Quit looking for icebergs.
Get back to work.
SK
That's the answer. If it was snug going in. it will be snug coming out. Ditto on ES post; just shoot it.
AJ
Thanks gentlemen.
Back to the range . . .