AR-15 not locking back on last round

Normally the carbon from the ammo will seal one off with time. The only ones I put any LocTite on is on SS barrels where everything shows. Then to get it apart requires heat to break down the Loctite. Now if it's reallying leaking bad it would not hurt any at all adding a sealant.

GDownRange said:

Well that could be my problem. I didn’t glue the rod into the block. I simply pinned the rod into the block. Is using adhesive to attach the rod to the block a common/recommended practice?

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Sorry, no, I didn't mean you should glue it in. I was talking about how the carbon deposits bond the gas tube to the block. You could hypothetically use something to seal up that leak, but I think that would be more of a diagnostic measure than a long term solution. There's some stuff that would be permanent, but then you wouldn't be able to ever use the gas block with a different gas tube length if you decided you wanted to change things up or recycle it on another build.

If you do try to seal it up as a diagnostic, be sure and use blue loctite. It's pretty easy to melt with a heat gun. Just be sure not to get any inside the gas tube or you'll end up with much bigger problems. I would probably avoid doing that in general. Much better to use those calipers and find out which part is out of spec. My money is on the gas block, as I've never heard of a gas tube being out of spec, though anything is possible. You might just call Odin Works and tell them what's going on and see what they say. I've dealt with them before and their customer service was good.

BTW, did you get a chance to measure the clearance between the bolt catch and the bolt face? Again, you want at least a nickel's worth.

Blue68f100 said:

Some gas leakage is expected, what you have is what most consider normal. If you have some true 5.56 ammo, your gun will probably operate since it runs at a higher pressure. But most all 556 ammo is tamed down some.

If your gas port is in fact 0.078" that is the min spec. This could be your problem. The spec range is 0.078-0.081" . The last barrel I made/turned and fitted, the min spec hole did not give enough gas to operate the bolt, just like your having. Drilling the hole out to mid spec corrected the problem. This is best done with number drills and/or reamers. I set mine up in my mill to drill it out. If you do this run a brass rod down the barrel to prevent from damaging it when you go through. Then you have to clean out the chips and any flashing still stuck to the barrel. A good fitting jag and patches works fine just takes several runs.

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.078 should be just fine. I've run smaller without any issues.

grampajack said:

They glue it in. And it only takes a few rounds to really cement one in there. To get it out without damaging it, you have to soak it in something for days.

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They glue what??. I've never seen or used glue on any AR

Check the alignment of your gas block port.
Check the gas key on your bolt and make sure it's tight. I once had a bolt carrier that short stroked the rifle. The key was staked properly but wasn't torqued and the gas leaked around it.
Which buffer are you running?
What type of ammo are you running?
Is this a mid length or carbine length?

carbine85 said:

They glue what??. I've never seen or used glue on any AR

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Read the thread! "They" refers to carbon deposits. No one is gluing anything.

Louca said:

Nobody has mentioned this yet, so here was my situation. On my rifle, I had exactly the same problem you are describing and tried everything you have been trying. I finally called the barrel company (Criterion) and asked them for advice. They said to drill the gas hole in the barrel a little larger.

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It was vetted a few times... Grampajack even went through some options for measuring the port dia... But there was a lot of stuff on the page to read, I guess you missed it...

BBBBill said:

Insufficient gas (port too small

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Varminterror said:

3) Insufficient bolt travel during cycle, typically due to improper gas system performance. This can be [...an...] undersized gas port,

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grampajack said:

Do you have any way of measuring the gas port? If not, can you contact the manufacturer and ask them what it should be, then perhaps verify it with a drill bit of that size?

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It was vetted a few times... Grampajack even went through some options for measuring the port dia... But there was a lot of stuff on the page to read, I guess you missed it...

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Thanks Varminterror for pointing that out to me. I must have read too fast and flew over part of Grampajack's advice. I will try to read better next time. What I wanted to say was that I did actually contact the barrel manufacturer regarding the gas port, and did drill the hole larger, and that it did solved my problem.

When I went through all that, I was a little nervous about having to drill a hole, since I had not heard of that ever being necessary. So looking back at Grampajack's advice, I hope my post sort of backed what he was advising and encouraged the advice by saying I did it and it worked for me.

Good for you and a good gas leak lesson for us all. I rarely have a gas tube go into the gas block without some resistance. Was the new gas block noticeably tighter on the gas tube (assuming the offending gas block was overbored)?