AR-15 bolt carrier unlocking issue.

[jrm]

Many years ago I bought a BCM upper that has sat unused. As I try to manually retract the bolt carrier it is “sticky” for the first bit of travel during what I would guess is the portion of travel related to the unlocking of the bolt after that it feels normal. Multiple bolt carriers and bolts exhibited the same behavior although I believe to varying degrees. At first it seemed the gas tube was sitting slightly askew and I thought that might have been the issue so I tightened the barrel nut a smidge. That seemed to fix the apparent off set in the gas tube. The stickiness improved little if any. I notice a bright spot around the front edge of the notch in the upper receiver for the cam pin but that seems common to my other AR that functions just fine. I see some minor machine type marking and a tiny bright spot on the bottom face of the 9 and 10 o’clock “lugs” of the barrel extension. Anyone have any recommendations on a fix? Shoot it and it will break in? Needs a new barrel\extension? Some sort of upper receiver defect and it needs a new upper receiver? I have yet to fire a round through it to know if it impedes function but it is definitely harder to manually retract the bolt compared to any other AR I have handled. Not impossible but harder than normal. Thanks for any input.

[Darth_Uno]

How’s it work with the upper removed? Could be the buffer or spring getting hung up.

[jrm]

Same when just the upper and removing the bolt carrier. Initially it is “stuck” apply adequate pressure and it slide right out. Here are some photos that may or may not be helpful.5114951150 Looking more it seems like the 6 o’clock lug also may have some of a bright spot to it.

[Clusterfrack]

This is likely a non-issue. I recommend adding a little grease to the bolt lugs, then lubing with oil.

I wouldn't have tightened the barrel nut on a BCM upper.

[jrm]

This is likely a non-issue. I recommend adding a little grease to the bolt lugs, then lubing with oil.

I wouldn't have tightened the barrel nut on a BCM upper.

Since tightening the barrel nut didn’t fix it I think I agree with you at this point. Barring anyone knowing what the likely issue is and how to fix it I think this is the path I will take. Thanks.

[rd62]

Have you tried running just the carrier without the bolt to determine whether its gas tube or bolt?

[jrm]

Have you tried running just the carrier without the bolt to determine whether its gas tube or bolt?

I have now. It’s less than completely satisfying but my primary BCM upper works fine with both the primary and secondary BCM BCG with or without bolt and same thing for my no name BCG. My secondary BCM upper sticks with the secondary BCM BCG with or with out the bolt same for my no name BCG. However, primary BCM BCG works just fine with or without a bolt in the secondary BCM upper. So I have a combo that is now working well in both guns just a bit odd that it takes a specific combo in what I would think would be plug and play. Anyway thank you for giving me another way of looking at the problem. I am guessing it’s just some minor tolerance stacking that would probably smooth out with use but the current combos appear to function check well. Thanks to everyone who chipped in.

[JohnO]

Lubrication is your friend. Aside from user error and magazines Lubrication, the lack there of, is the #1 cause of malfunctions. Run it wet.

[Wake27]

Wait, so you’ve never even shot it but it felt off to you so you started messing with it?


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[jrm]

Wait, so you’ve never even shot it but it felt off to you so you started messing with it?


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Yes it was a very noticeable sticking. Some what painful at first to pull on the charging handle hard enough to free it. Very different from normal but not impossible to cycle by hand.

[Wayne Dobbs]

Since tightening the barrel nut didn’t fix it I think I agree with you at this point. Barring anyone knowing what the likely issue is and how to fix it I think this is the path I will take. Thanks.

Since you tightened the barrel nut, did you go through the steps to make sure the gas tube, upper, barrel nut and gas carrier key tube were properly aligned?? You don't just tighten the barrel nut without consequence and there's now a good chance you've bent the gas tube and/or created an impingement failure point at its contact with the barrel nut.

[jrm]

Since you tightened the barrel nut, did you go through the steps to make sure the gas tube, upper, barrel nut and gas carrier key tube were properly aligned?? You don't just tighten the barrel nut without consequence and there's now a good chance you've bent the gas tube and/or created an impingement failure point at its contact with the barrel nut.

I removed the front sight block with the tube attached prior to tightening then reinstalled. It appears straight and evenly spaced in side the upper receiver at this time. Prior to doing this the gas tube seemed slightly angled and the notch in the barrel nut seemed ever so slightly under tightened to properly align. It did not need to be forced in but I do not know what the procedure would be to ensure it was not bent in the first place or to make sure I have not damaged it. It seems to function properly by hand with a quality BCG but not all quality BCGs at this point. I wish I had just contacted the manufacturer on day one but I didn’t and now I truly do appreciate the help.

[Wayne Dobbs]

I removed the front sight block with the tube attached prior to tightening then reinstalled. It appears straight and evenly spaced in side the upper receiver at this time. Prior to doing this the gas tube seemed slightly angled and the notch in the barrel nut seemed ever so slightly under tightened to properly align. It did not need to be forced in but I do not know what the procedure would be to ensure it was not bent in the first place or to make sure I have not damaged it. It seems to function properly by hand with a quality BCG but not all quality BCGs at this point. I wish I had just contacted the manufacturer on day one but I didn’t and now I truly do appreciate the help.

To do an at home alignment/bent tube check of the gas tube, strip your BCG until you have only the bolt carrier. Remove the charging handle and slide the bolt carrier into the upper while holding it horizontal. Then tip the upper up about 20-30 degrees and your bolt carrier should slide over the gas tube with no friction, clicking or stopping. If it does that, you should be good.

[Clusterfrack]

So, this is a BCM upper? How did you remove the gas block? Typically the set screws do not come out easily. Or at all.

[jrm]

To do an at home alignment/bent tube check of the gas tube, strip your BCG until you have only the bolt carrier. Remove the charging handle and slide the bolt carrier into the upper while holding it horizontal. Then tip the upper up about 20-30 degrees and your bolt carrier should slide over the gas tube with no friction, clicking or stopping. If it does that, you should be good.

Definitely some friction and stopping no clicking. I will order a new gas tube. Thanks.

[jrm]

So, this is a BCM upper? How did you remove the gas block? Typically the set screws do not come out easily. Or at all.

It is a traditional FSB with taper pins I used a cupped punch, hammer and brownells branded block.

[Wayne Dobbs]

It is a traditional FSB with taper pins I used a cupped punch, hammer and brownells branded block.

Sometimes that makes lots of noise and cuss words!

[jrm]

To do an at home alignment/bent tube check of the gas tube, strip your BCG until you have only the bolt carrier. Remove the charging handle and slide the bolt carrier into the upper while holding it horizontal. Then tip the upper up about 20-30 degrees and your bolt carrier should slide over the gas tube with no friction, clicking or stopping. If it does that, you should be good.

Ok barrel nut re-torqued and timed new gas tube installed and all appears right with the world now. My guess is the gas tube got bent at some point and my barrel nut shenanigans were unnecessary and counter productive. It came without hand guards so it was vulnerable from BCM QC, at which point I’m sure it was in good working order, until I got the hand guard installed. Anyway thanks Wayne and all who helped out.