9mm AR15 build is unreliable ... headspace issues?

[jeffmem]

A few years ago I built a 9mm AR15 consisting of the following parts:

RRA 9mm flattop upper CAR length with bolt/carrier

9mm Hammer

Hahn dedicated top load mag block

Promag polymer 9mm magazine

9mm buffer

Before I fired the first round I put a knights armament CQB quad rail on it. Usually I can fire 3-5 rounds and then it jams and last week when I shot it it was pushing bullets back in to the brass when it jammed. When I inspect the brass it does fire it looks like gas is getting around it the cases they are significantly discolored with carbon.

I dont know if this is the cause of the unreliability or if it is something else. Can a 9mm AR15 have headscape issues if the barrel is not torqued to spec?

[JeffsSig]

Sounds like a buffer and or buffer spring issue.

[Magiccarpetrides]

You might also want to try a different brand of magazine. Typically promag can't make a reliable double stack to save its life.

[Reservoir Dog]

You might also want to try a different brand of magazine. Typically promag can't make a reliable double stack to save its life.

+1

Promag makes crappy mags. Definitely try a different brand of magazine. Get some Colt mags, if you can find them. If not, try some from Spikes Tactical or C Products.

With a factory RRA upper, I doubt headspacing is an issue.

Edited March 27, 2011 by Reservoir Dog

[jeffmem]

I am going to try a new magazine. The blackened brass is normal from what I read on another board.

[Magiccarpetrides]

I think aimsurplus.com had some under the magazines section

[jeffmem]

I should have a couple of new ones in this week.

[Reservoir Dog]

Also, make sure your Hahn mag block is in good order, and installed correctly.

[jeffmem]

Bought a metal c-mag and ran 300 round flawlessly. Promags need to visit the sawzall

[Capbyrd]

Glad you got it worked out sir. Better to see something like this fixed than sold off.

[Dolomite_supafly]

I am pretty sure I mentioned the CProducts in your ad when you where trying to sell it.

Glad it worked out. My, actually the wife's, 9mm AR has at least 7,000 rounds through it. You get soot around the casing, it is the nature of the beast with any blowback gun. As far as the bullets getting pushed back into the case, that is caused when the round hits the edge of the chamber. This is generally caused by a magazine not sitting right.

I will say if you start having problems again clean the mags first. They get full of crap because of the blowback and will cause issues similar to using a ProMag.

Other that the issues you have worked out, which I had also, my wife's AR has been fun and reliable. And BTW, it is the easiest gun to bumpfire I have ever tried.

I dont know if this is the cause of the unreliability or if it is something else. Can a 9mm AR15 have headscape issues if the barrel is not torqued to spec?

No, the headspace is set by the recess in the bolt and the chamber itself. When the bolt is resting on the rear of the barrel that is where the headspace is set. There is no adjustment to the headspace on your gun. And if the barrel were loose you could theoretically still fire it with no headspace issues.

Dolomite

Edited April 4, 2011 by Dolomite_supafly