Getting some short stroking, couldn’t figure out why then I noticed carbon fouling out the front of the gas block.  Block is pinned and tight but either out of spec block or barrel.

Any creative ideas on how to fill in the loose tolerance?  I have access to most tools. My knee jerk was to weld it shut quick but there’s got to be a less dramatic solution.

Thanks

The easiest thing to do in my opinion would be to remove the gas block and replace it, could also break out the calipers and see if the barrel diameter is undersized or if the gas block is oversize and replace whichever one needs replaced and look for any other problem indicators like excessive gas port erosion. Parts make? Any pics? Is this a homebrew or do you have a factory gun/upper that you might be able to get support for?

Removing the gas block won’t be hard if you have some punches, a decent weight hammer, a block to punch the pin(s) into/support the barrel and gas block, you can make a gas block/front sight block removal support pretty quick out of 2x4 scraps too, suggest wrapping the upper receiver in a towel or something soft while you drive the pin out or remove it if you go that route and have the tools needed already.  

As far as creative solutions for reusing the block or barrel whichever is the problematic part I’m out of idea’s, I realize that it would be a pain to have to shell out cash on a new barrel or gb but not sure how else you would seal it properly.
Could be a good excuse for a rebuild/new look!

Locktite green - it creeps into the cracks. not too much and shoot the gun when you do it to make sure the hole stays clear.

What it doesn't seal up the carbon will seal up eventually.

JMHO, if the tolerances are "close enough", the observed "carbon fouling" itself will eventually seal the leaks.  i.e. shoot it some more.

Getting some short stroking, couldn’t figure out why then I noticed carbon fouling out the front of the gas block


Since it's short stroking waiting for carbon to seal it is pointless.


Either replace the GB or seal it with retaining compound.

What ammo is short stroking? If the gas block is properly aligned it should work 100%.

Try some of that HVAC duct work aluminum tape, I wonder if you could put a very thin layer around the  gas port and slide the gas block over that?  That would mean you have a big size difference.  I think they make different thicknesses of that aluminum tape.

I could buy a new barrel and gas block but this is a beater rifle, fixing it is more of something to do.

I thought the same thing- just shoot it until it closes itself up but I put around 100 rounds through it to no avail.

Maybe JB weld?  I'm skeptical any bonding compounds will hold- seems like the intense pressure will just blast it right off.  This is why my mind initially went to weld / stake the gas block/barrel area where the carbon fouling is most prominent.

Loctite 648

When you blow air down the gas tube do you feel air coming out of the barrel? You should feel a very strong flow of air coming in.

My thought is the gas block isn't aligned and the excessive carbon you see is the result of carbon blowing out from where it is being blocked (path of least resistance).

You got the answer 5 posts above!

While i agree that eventually carbon should plug the gap, and loctite will plug the gap now, I'd be more concerned about the gas block being in spec, the gas block journal being in spec, the gas block being properly aligned, the gas key being properly torqued, the ammo isn't shitty, the spring is standard weight and the buffer is standard carbine or rifle weight. I'd also want to inspect magazines and also note if this happens on first round of fully loaded magazines only or more often than not. I just don't see the point in sealing up an underlying problem.

@d5griffin ...A few quick questions:
Can you post a photo?

Who makes the barrel?

Did you put a caliper on the gas block journal?

Did you confirm you have the right size gas block before assembly?

What's the barrel length?

Any idea on your port size

Who makes your gas block?

What material is the gas block manufactured from?

Did you align the gas block with the gas port before you tightened it down?

What ammo are you shooting?

What recoil spring, buffer and bolt carrier group are you using?

What mags are you using?

I appreciate the thorough nature but I don’t have a ton of answers.

Tac swap No-name barrel, GB no idea, found in parts bin.

Again I have plenty of ARs, this is an academic exercise.

Will try green loctite and report back, not sure when I’ll have time for range though

NVM, not relevant.

Once you put that block on with green Loctite, you're not getting it off without a whole lot of heat. I would start by making sure the gas block and the port are aligned correctly. Some barrels are made for a low-pro gas block to set up against the shoulder, and others are made for the block to set off the shoulder 1/10" or so. The easiest way to do it is to make sure the port hole in the block lines up with the rear set screw hole. If it does, flip the block over and center the set screw hole over the gas port in the barrel. Mark the barrel where the front of the block is, flip the block back over, and lock it down.

Are you sure it’s not the gas key on the bcg or something else.  If the block is the correct size and centered over the gas port the problem may be elsewhere