AR9 troubleshooting

[teamRR]

I have a spare lower here, initially didn't try it because I couldn't quite get the upper to fit, was tight on the rear lug. Took me about 5 minutes of working the upper in and out, a quick pass of a file to remove anything sticky and its matching up now..

I checked the fit of the BCG & CH and nothing hangs on the ejector with this one. Also noticed the ejector has a slight angle left on the spare where the original that's falling points more parallel.

I think next test is to put some parts in this one and try it. If I find its reliable I will then know how the ejector is supposed to look.

 

[boilermaker]

Any chance to get back to the range with this?

 

[teamRR]

Any chance to get back to the range with this?

Yes, I owe some updates.

Sooo the 2nd lower had the exact same problem.

Didn't seem to matter what spring or buffer combination.

I then bent the ejector to the right a bit on the original lower and it has been about 100%.

One detail I also found is one of my metalform mags was giving an intermittent 2nd to last round bolt hold open. Occasionally when this happened the last round would end up in some odd state from just floating around in there. Turns out the tab that actuates the bolt stop is a little longer or a little out of position on that one mag.

So I am still in somewhat of a testing & tuning phase but I have about got it.

 

[boilermaker]

Have you tried it with Colt mags? It is odd that you got through 100 rds no probelm and them problems started to ensue but I suspect it mag related

 

[teamRR]

Have you tried it with Colt mags? It is odd that you got through 100 rds no probelm and them problems started to ensue but I suspect it mag related

Only mags I have are Metalform, which are supposed to be really good to go but I don't know from experience. Even when I tried to buy another brand (bought some Yankee Hill) they showed up as Metalform stamped in YH packaging. Actually would have probably bought some brand name Colt but they haven't been available (though it wouldn't surprise me to find they are MF too)..

No matter how I look at it really doesn't add up that everything worked so well right up to that 100 rounds then failed so often (ie 10%) across the 5 different mags I'd been using. Everything other than the upper itself was swapped out, two different BCG's and another lower, springs and buffers etc.

The only half plausible scenario I can makeup is the ejector wasn't quite right then was knocked out of its original position just enough the wrong way to induce failures - the ejectors in these are not positively pinned in position, there is a little play present on the securing allen and friction keeps them from seeming "loose", so could be jarred a bit one way or the other.

The only thing that solved the problem, and very consistently so far, has been timing the ejector right a touch, which is something I read on another forum as the fix to such problems.

Anyway so yes its hard to understand no matter what way you look at it given it worked so well initially.