10.5" Pistol upper issue

[ASH556]

I've begun working Saturdays at the LGS again and being the most well-versed behind the counter in AR's as well as having completed IG's armorer's course, I generally get all the AR questions. The shop also has an indoor range attached, so we get more than our fair share of screwed up guns to deal with (usually it's a simple, on-the-spot fix).

So last Saturday a guy comes in and his AR pistol won't run...now...I sold this guy a YHM diamond handguard earlier in the morning and talked through his application with him...it's a cobbled-together parts gun with less-than-stellar parts. The barrel is a Model 1 Sales 10.5" and I have no doubt that it's overgassed. He was running it with a carbine RE, Carbine spring and carbine buffer. The BCG was a neutered 1/2 circle, non-shrouded firing pin older colt. The malfuction (on every single round) was a failure to eject. I assume it's a bolt speed issue because the ejector has good tension and is not binding.

When feeding from a loaded magazine, you experience the bolt picking up a new live round from the magazine while still holding the empty case. When feeding the last round from a magazine, the bolt does lock open on empty, but the case is floating loose inside the upper receiver.

I also tried the upper on my DD MK18 lower with H buffer...same issue. I recommended he try a heavier spring with an H3.

Assuming he's there tomorrow and the spring/buffer combo doesn't fix the issue, is it safe to assume it's still just super-over-gassed (insertable gas port, new barrel) or am I missing something else?

Thanks!

[Iraqgunz]

Model 1 barrels are crap. I would measure the port for shits and giggles. I'd be interested to know about the chamber as well.

Have you considered isolating the source by putting another BCG in there?

[ASH556]

Model 1 barrels are crap. I would measure the port for shits and giggles. I'd be interested to know about the chamber as well.

Have you considered isolating the source by putting another BCG in there?

Yeah, I politely mentioned the lack of quality of Model 1 barrels and he agreed but, "got it for a good deal.":rolleyes:

I just now realized that my post isn't clear that I don't have possession of the upper anymore. If he brings it in again I'll swap BCG's and see what happens. If he leaves it with me, I'll tear it down and measure the port (I'm betting it's at least in the 8's, maybe even the 9's).

You'd be proud, though, I did an end-plate swap for a guy (he supplied the part, some slap-plate looking thing) and staked it in two places and explained why I was doing so...he was a local cop and very grateful.

[MistWolf]

Ash, if I'm following you, the upper extracts but does not eject.

Is it possible that the extractor is holding the case too tightly?

Or, is it possible the extractor isn't holding it against the bolt face tightly enough and thus not compressing the ejector properly?

Is it possible the ejector is too short?

A really long shot- Is it the bolt face cut for the 5.56 or is it possible it's the wrong bolt, say for a 6.8 or 6.5?

Does the rifle eject when cycled by hand?

[ra2bach]

I've begun working Saturdays at the LGS again and being the most well-versed behind the counter in AR's as well as having completed IG's armorer's course, I generally get all the AR questions. The shop also has an indoor range attached, so we get more than our fair share of screwed up guns to deal with (usually it's a simple, on-the-spot fix).

So last Saturday a guy comes in and his AR pistol won't run...now...I sold this guy a YHM diamond handguard earlier in the morning and talked through his application with him...it's a cobbled-together parts gun with less-than-stellar parts. The barrel is a Model 1 Sales 10.5" and I have no doubt that it's overgassed. He was running it with a carbine RE, Carbine spring and carbine buffer. The BCG was a neutered 1/2 circle, non-shrouded firing pin older colt. The malfuction (on every single round) was a failure to eject. I assume it's a bolt speed issue because the ejector has good tension and is not binding.

When feeding from a loaded magazine, you experience the bolt picking up a new live round from the magazine while still holding the empty case. When feeding the last round from a magazine, the bolt does lock open on empty, but the case is floating loose inside the upper receiver.

I also tried the upper on my DD MK18 lower with H buffer...same issue. I recommended he try a heavier spring with an H3.

Assuming he's there tomorrow and the spring/buffer combo doesn't fix the issue, is it safe to assume it's still just super-over-gassed (insertable gas port, new barrel) or am I missing something else?

Thanks!
sounds like the ejector not the extractor. did you check the spring?