Unlocking problems with unfired upper; What should I check for before sending it back?

[Naaman]

Hello All,

Update to issue, see post 26.

I'm about this close to sending back an upper receiver (mil-spec). It was shipped from the factory with barrel and hand guard installed. Upper was test fired at the factory. I added a BCG and CH both from the same manufacturer.

When manually cycling the action with no ammo, everything works fine. When doing so with rounds (either dummies or live), the bolt seems to fail to unlock when pulling the charging handle using the expected amount of force. The charging handle latch will actuate, but the bolt will not move. If I use a greater amount of sudden force, the action will cycle.

Some things I have noticed include brass on the bolt face, and scratches/gouges on the jackets of the bullets (and in one case, on the casing; may have been from a user induced double feed). Ammo is BH 262.

I tried swapping CH and BCG into other uppers. Everything works as expected. I tried swapping two different known good CHs and BCGs into the new upper, and the problem persists.

My research so far makes me think this might be a headspace problem (headspace gauges on order now).

What can I do/check at home before getting the manufacturer involved? Anything else it could be other than out of spec?


Some additional details in case they matter:
I'd like to avoid sending it back if possible because I'm really ticked off about the way shipping companies have been handling packages lately (the upper in question is hard to get). I also don't like "not having" my life saving tools on hand.

I'm also trying to learn more how to deal with these kinds of things on my own, so I don't mind at least going through a diagnostic process if not just fixing it out right.

I'm considering just going to a local smith if anyone can recommend one in Arizona.

 

[The King]

Clean the fuck out of the chamber.

Some chambers have shit in them like a hard brown crust from dried coolant. If you have a bore scope you can look even better.

 

[Keeper22]

Sounds like a chamber problem, either as posted gunk built up, but if it's that bad you should see it on the ammo. A very thorough cleaning never hurts. I would definitely check the head spacing before firing it. The head scratcher is the factory test fire, if they actually did it, head spacing issues should have shown up immediately. Keep us posted.

 

[hlee]

I have a barrel/bcg from one maker who warned that the bolt would feel “sticky” when manually cycling, until it was worn-in from firing. He was right, but after a couple of mags, no issues with actual live fire function.

 

[TheOE800]

Shoot your gun.

 

[hlee]

Shoot your gun.

Think of the RESALE. Come on, man…

 

[Naaman]

I was wondering if it needed to be shot. Its my first time aggregating parts into a whole build, so I don't know what I don't know, you know?

I will try cleaning it out.

I have a range trip planned next week to sight it in, but wanted to be sure I don't have a safety issue before just doing what Bubba would do. Lol.

 

[UpSideDown]

Are your bullets engaging the rifling?

 

[Naaman]

Are your bullets engaging the rifling?

Hmm... Not sure. How would I find out?

 

[Milf Dots]

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[flatsix-]

I had this with a 6.5 gas gun. Was diagnosed as having a slightly off center index pin on the barrel which caused a little drag in unlocking. Manufacturer replaced the barrel and no further issues.

 

[Makinchips208]

I had this with a 6.5 gas gun. Was diagnosed as having a slightly off center index pin on the barrel which caused a little drag in unlocking. Manufacturer replaced the barrel and no further issues.

Was it smooth or did it also have the problem with NO ammo in the gun, like the op has? Or did it do it regardless of a round in the chamber or not?

 

[flatsix-]

Was it smooth or did it also have the problem with NO ammo in the gun, like the op has? Or did it do it regardless of a round in the chamber or not?

Regardless of round in chamber. To pull on the charging handle slowly there was resistance, not smooth like it should be. The difference with the new barrel was marked.

 

[Naaman]

Was it smooth or did it also have the problem with NO ammo in the gun, like the op has? Or did it do it regardless of a round in the chamber or not?

No, mine works fine empty. Only when ammo is chambered does the problem present.

 

[flatsix-]

No, mine works fine empty. Only when ammo is chambered does the problem present.

That’s interesting. Have to say I would send it back and let them deal with it. It’s good to self diagnose and fix small issues but comes a time where the manufacturer needs to step in and make their stuff right. I wish you luck with it.

 

[Makinchips208]

No, mine works fine empty. Only when ammo is chambered does the problem present.

But it will lock the bolt in and extract without hammering on it? In that case it will smooth out with use.

 

[Naaman]

Another data point is that the rounds fall free when I hold the muzzle up.

One of my coworkers who knows much about these things agrees with the overall consensus here regarding cleaning it out and just shooting it. After the weekend, I should get a response from the manufacturer.

 

[Milf Dots]

If you can, post some close up pics of the feed ramps and chamber. Perhaps someone might see something.

 

[hlee]

Clean it. Lube it. Shoot it. Report back if it fails to function. Don’t be totally surprised if it takes a couple of mags to get going, especially if the chamber needs burnishing.

 

[Naaman]

If you can, post some close up pics of the feed ramps and chamber. Perhaps someone might see something.

Good idea. That has helped before. I'll take some pics tomorrow or next day.

Clean it. Lube it. Shoot it. Report back if it fails to function. Don’t be totally surprised if it takes a couple of mags to get going, especially if the chamber needs burnishing.

I'm kinda expecting it to at least extract since I can manually cycle it. Just struck me as odd how much force it took to "break" past the internal resistance (it's not linear, like everything else I've used). I should know by the beginning of next week.

 

[hlee]

Good idea. That has helped before. I'll take some pics tomorrow or next day.



I'm kinda expecting it to at least extract since I can manually cycle it. Just struck me as odd how much force it took to "break" past the internal resistance (it's not linear, like everything else I've used). I should know by the beginning of next week.

I have a barrel that required me to use a finishing hammer to remove cartridges for the first dozen or so shots. Cases were stuck so hard that mortaring the gun didn’t budge the carrier. Tap, tap, tap on the charging handle broke them free. It went from not unlocking at all, to extracting a little, to short stroking, to full ejection over about 30 shots. Now, extraction is fine, but-as a Grendel variant- magazines are a toss up. It shoots tiny little groups, but occasionally loading will break the polymer tip of an eld-m clean off and throw it somewhere into the works (like into the locking lug recess) and jam everything up. I need to switch to SMKs or the like, but I’ve got a lot of the Hornady bullets.

 

[JohnCarter17]

I have a barrel that required me to use a finishing hammer to remove cartridges for the first dozen or so shots. Cases were stuck so hard that mortaring the gun didn’t budge the carrier. Tap, tap, tap on the charging handle broke them free. It went from not unlocking at all, to extracting a little, to short stroking, to full ejection over about 30 shots. Now, extraction is fine, but-as a Grendel variant- magazines are a toss up. It shoots tiny little groups, but occasionally loading will break the polymer tip of an eld-m clean off and throw it somewhere into the works (like into the locking lug recess) and jam everything up. I need to switch to SMKs or the like, but I’ve got a lot of the Hornady bullets.

I hope and expect this is the case for me. I took 2 Grendels out for their first firing.

A pistol build with a Lilja 10.5" barrel and just a cheek support (no brace). I have a bunch of Wolf I got a few years ago and consider it suitable for break in.

So the 1st round ejected but it didn't load, the 2nd round didn't cycle the bolt. And it smacked me in the nose (Swampfox Trihawk 3x prism). I was able to cycle with the CH and cleared it and put it away. It's not for me in that configuration, maybe ideal with a different caliber, or I play with the gas or whatever.

The second is a 16“ Lilja. The first round never ejected and it's on their tight. I'll try tappity tap on the CH to get it out.

Mind you, both are with the AGB not tuned yet.

 

[Evintos]

Assuming headspace checks out and parts aren't out of spec.

Here are three things that could be happening.

If it's a nitrided barrel, the black oxide is providing a little bit of excess friction. This goes away after cleaning and firing a few rounds.

The other thing is headspace is closer to the minimum side, the bolt lug contacts the rear of the barrel extension with a cartridge chambered vs no cartridge chambered. You'll see finish wear on the back face of the bolt lugs if this is the case and you can sometimes feel this when you insert the bolt into the extension and rotate by hand to see if it spins freely vs feeling some friction. This can also happen if you have a barrel extension with slightly too thick of a layer of NiB. If the layer is not too thick to be a permanent issue the mating surfaces will wear in.

Concentricity issues caused by the cartridge present in chamber resulting in a little bit more friction. You'll see finish wear more along the top edges of a few lugs on one side versus the other side. Usually not an issue once the mating surfaces break in. Theoretically the lugs that receive the most wear would be the first to break if you shoot enough rounds to wear out several barrels.

You can help the process along by manually cycling the action and letting the BCG slam forward under spring pressure about a hundred times but really shooting is the fastest way.

Scratches on the body of the cartridge particularly by the neck and shoulder as well as scratches on the bullet can also come from sharp feed ramp corners.

 

[flatsix-]

It's definitely worth ruling out headspace issues before going back to the maker. Easy enough to do and you mentioned you have the tools on the way. I am assuming this is an AR-15. I feel like the way the industry is today, it's piss easy to make a functioning AR-15 so why suffer chasing down more complicated issues?

 

[Naaman]

Got out to the range today. However, I forgot to inspect the brass because I spent 3/4 of the time training my sons (good times).

Upper shoots fine, no issues with operation (albeit, I only fired about a mag worth of IMI razor core).

I tried to shoot for groups, but a 3x with a 2MOA dot at 100 is pretty tough (for me). One more reason to look at dropping the dough on a LPVO or maybe a 5x magnifier. Anyway, the grouping at 100 was nothing to write home about. 2-ish MOA... maybe. I believe the gun can do better, but my sighting system just was not up to it. At 50 I was able to "call" a "miss" that was about 1/2 MOA off target because I broke the shot slightly later than I "intended" to (still within the bullseye, but not exactly on center; that was my 2-shot group to confirm zero). In any case, it seems like everything is fine and the ammo probably isn't being adversely affected by anything in the barrel/chamber.

I got a return authorization from the MFR, but I think I'll take it out one more time just for peace of mind before deciding to send it in.

Thanks for all the input. It took a burden off my shoulders.