9mm AR-15 issue - case head separation

erwos · May 30, 2017

So, I took out my recent "DDLES 9mm Glock lower + PSA Hybrid upper" build to AGC the other day for test-firing, and had some issues with case-head separation. One possibility is that it's because I was using Freedom Munitions ammo, which sometimes uses so-so cases... but I've never actually seen it happen in any of my other 9mm blowback carbines, to include another 9mm AR-15. The other possibility I can think of is that extraction is happening too quickly (which might be exacerbated by FM's cases, I guess).

This particular build is using a good 9mm heavy buffer (8.5 or 9oz, I forget) that's the appropriate length. Assuming this is an "extraction too fast" issue, are there any heavier springs I should try that people can recommend?

Also, if anyone's got any tricks to dig out the half case that's left in my chamber, I'd appreciate it.

No one makes a 9mm broken shell extractor for some reason...

SKIP · May 30, 2017

I would try any rifle broken case extractor close to 9MM.

clandestine · May 30, 2017

I have experienced head separation issues with that ammo. Cerrosafe is what I use to remove to remove head separations from Chambers.

As far as springs, use a tubb flat wire spring for a .308 for blocback 9mm's.

Headspace could be off as well.

GolfR · May 30, 2017

Have you tried dropping an unfired round into the chamber to see if the round full seats and falls out of the chamber freely? If you have to jam the round in (which you may not notice because the bolt is closing with force) then you may have a headspacing or chamber issue on the barrel.

Are you flattening primers or the cases showing other indications of over pressure?

erwos · May 30, 2017

clandestine said:
I have experienced head separation issues with that ammo. Cerrosafe is what I use to remove to remove head separations from Chambers.

I had sort of hoped to avoid Cerrosafe, but it doesn't look that hard to use. If I can't use a cleaning brush to get it out, that's the next step, I imagine.

As far as springs, use a tubb flat wire spring for a .308 for blocback 9mm's.

I'm on it. Thanks for the recommendation.

Headspace could be off as well.

Definitely possible, knowing PSA. I'll hunt up some gauges... I've got so many 9mm handguns and rifles that I probably owe it to myself to check them out.

GolfR said:
Have you tried dropping an unfired round into the chamber to see if the round full seats and falls out of the chamber freely? If you have to jam the round in (which you may not notice because the bolt is closing with force) then you may have a headspacing or chamber issue on the barrel.

Are you flattening primers or the cases showing other indications of over pressure?

I had been using a laser trainer cartridge in the chamber with no problems, so I don't think it's a tight chamber. Fired primers looked pretty normal to me, no overpressure signs that I noticed.

Magnumite · May 30, 2017

My son's friend had this same issue with FM ammo in his 9mm AR. Only refraining from using FM fixed the problem.

FM has issues in more than one caliber.

photoracer · May 30, 2017

Trust me if you are using a PSA 9mm barrel it will not like ammo that is over 1.13" OAL. Anything longer can get stuck in the rifling and pull the round apart when clearing the chamber manually. I followed some advise and bought a throat reamer from Brownell's and cut the rifling farther down into the barrel. Still working on how long an OAL I want to cover.

E.Shell · May 31, 2017

Cerrosafe is for other stuff...

Try this:
Push a .40 brush up into the cartridge case until the bristles are fully inside the broken section of 9mm. Unscrew the rod, leaving the brush in the case. Put a jag on the rod tip and now go in from the other end and push the case out from the muzzle.

The oversize brush will not reverse inside the broken case, giving you something to push against...

If you can't get the case out, the .40 brush will drive on up the bore, but I have used this trick 15-20 times with great success.

outrider58 · May 31, 2017

E.Shell said:
Cerrosafe is for other stuff...

Try this:
Push a .40 brush up into the cartridge case until the bristles are fully inside the broken section of 9mm. Unscrew the rod, leaving the brush in the case. Put a jag on the rod tip and now go in from the other end and push the case out from the muzzle.

The oversize brush will not reverse inside the broken case, giving you something to push against...

If you can't get the case out, the .40 brush will drive on up the bore, but I have used this trick 15-20 times with great success.

I'm gonna remember that one and pray I never have to use it. Thanks for the tip Ed.

erwos · Jun 1, 2017

E.Shell said:
Cerrosafe is for other stuff...

Try this:
Push a .40 brush up into the cartridge case until the bristles are fully inside the broken section of 9mm. Unscrew the rod, leaving the brush in the case. Put a jag on the rod tip and now go in from the other end and push the case out from the muzzle.

The oversize brush will not reverse inside the broken case, giving you something to push against...

If you can't get the case out, the .40 brush will drive on up the bore, but I have used this trick 15-20 times with great success.

I just used the .40 brush and it came right out. Apparently it wasn't stuck too badly.

erwos · Jun 2, 2017

New wrinkle: When I tried to install my new Tubbs 308 spring in this 9mm AR-15 with carbine-length buffer tube, it didn't seem to fit. It seemed to compress itself fully before it went all the way in. Do I need to trim the coils?

clandestine · Jun 2, 2017

erwos said:
New wrinkle: When I tried to install my new Tubbs 308 spring in this 9mm AR-15 with carbine-length buffer tube, it didn't seem to fit. It seemed to compress itself fully before it went all the way in. Do I need to trim the coils?

Something is off. The .308 flat wire spring is shorter when compressed to solid height than a standard carbine spring.

Perhaps the diameter of the buffer is binding on the hole in the tubb spring? Sometimes the buffer pad roll pin can be the cause

outrider58 · Jun 2, 2017

clandestine said:
Something is off. The .308 flat wire spring is shorter when compressed to solid height than a standard carbine spring.

Perhaps the diameter of the buffer is binding on the hole in the tubb spring? Sometimes the buffer pad roll pin can be the cause

Mine went right into my short(carbine length) pistol tube without problems. Two different ones as a matter of fact. Something is rotten in Demark.

erwos · Jun 3, 2017

Odd. I'll screw with it more tonight and tomorrow.

EDIT: Got it in. Just required more elbow grease than I expected.

erwos · Jul 10, 2017

Final update: I took my upgraded rifle (new buffer spring, new ejector) out to the range yesterday to function-test and zero it. No issues (other than discovering Magpul Glock mags don't lock in without pounding them in). Made sure to use IMI 115gr exclusively, so I guess either better ammo or the 308 buffer spring did the trick. Many thanks to everyone for their advice!

clandestine · Jul 10, 2017

Great news

9mm AR-15 issue - case head separation

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