[lowepg]

AR pistol (5" barrel)

Shooting some older chicom ammo (Norinco green box) and the the brass was the most distorted Ive ever seen:

http://farm9.staticflickr.com/8465/8078370152_b602db3f31_c.jpg

stopped after about 6 rounds but they were ALL bulged.

tried Winchester white box and American Eagle ammo immediately following and didnt see the issue...

[Deus Machina]

Get your gun checked, yesterday.
The ammo may not be the best but there is NO WAY it would look like that if it was chambered properly when fired.

[Rail Driver]

I'd have to agree that the ammo wasn't fully chambered when it fired - I wouldn't jump to the conclusion automatically that it's the gun's fault, however. If factory new ammunition fires fine with no problems, then the ammo was likely at fault - being old chicom surplus, the ammo was probably out of spec for a chamber that is at the tight end of being within specifications, and likely had brass that may be a bit softer than new stuff.

[lowepg]

Upon closer review the hammer pin broke (Its an AR15 carbine) as well. I cant tell if it happened before or after...

Noticed the trigger not resetting properly... saw the pin fell out and the hammer was sliding around a bit in the lower...

ARG. I wouldnt think this would CAUSE the bulging, but maybe super hot ammo caused the break?

[tightgroup tiger]

I looks to me like the the cartridge is firing before being completely in the chamber.

Does this AR 9mm pistol have a free floating firing pin? I'd check the firing pin if I were you.

[k_dawg]

Yikes.

The firing pin is 'firing' while the bolt is out of battery. Badly out of battery. We're not talking about a 0.05" in a headspace issue.

BAD BAD BAD

[Rail Driver]

I wasn't talking about a minor ~.05" headspace issue. Out of spec ammo in a tight chamber could result in the cartridge stopping .25" or more out of the chamber (as shown by the bulged brass). Combine that with a free floating firing pin and a bolt carrier moving at a high rate of speed and maybe softer pistol primers and you've got out of battery firing resulting in said bulged cases. AR-15's (at least every one I ever had experience with) have free floating firing pins. I would be wondering if the bulged cases striking the hammer at speed on the way out of the gun could have caused enough lateral stress on the pin to break it if it was a lower quality part. I've seen weak pins with DPMS, Del-Ton, and similar "budget" LPK pins, and it's usually the hammer pin that breaks.

[lowepg]

Well, before I noticed the broken hammer pin- i got a couple "doubles", but that was after i switched from the chicom stuff to the winchester ammo. I collected all that ammo (maybe 30 pieces) and none had that bulging....

grabbing the rest of the box and testing them in the rifle chamber now...

or should i use a reloading case gauge?

[lowepg]

The chicom stuff is MUCH tighter in the ar chamber... a few pieces were even snug in my glock chamber- and those are pretty sloppy.

So, i think the ammo may have contributed to the issue.... also did a web search on Norinco 9mm and found a few threads with people complaining about VERY hot loads and spotty specs.

by comparison, the WWB ammo dropped in MUCH smoother and "clicked" easily into the chamber...

[Rail Driver]

There's your answer then. Personally I'd invest in a higher quality lower parts kit when you order your replacement pin, and leave the norinco ammo alone, or save it for the Glock.

[paintballdude902]

your gun is firing before the bolt is fully into battery.

a weak shell and you will be spraying burning powder out possibly get a squib or worse

dont shoot it anymore till its fixed.

[Certaindeaf]

That loooks like some dang good brass. Count yourself lucky.

[lowepg]

There's your answer then. Personally I'd invest in a higher quality lower parts kit when you order your replacement pin, and leave the norinco ammo alone, or save it for the Glock.

What's my answer?

[mokin]

Good thing nobody was hurt!

I had some silver box Norinco 9mm that was very "unreliable" too. Every other round I had to manually cycle the action due to a failure-to-extract stoppage on an older HK. I also tried it in a Browning that I thought was much easier to feed. That resulted in blown primers and the beginning of the end for the recoil spring guide. I picked up the brass with the intention of handloading it but found that a lot of the primers would not remain in pockets. I dicided to put all the other Norinco ammunition a side to break down and rebuild at some future date when I have absolutely nothing better to do.

Stop shooting the Norinco ammo and rebuild your lower.

[exavid]

Agree with all, firing out of battery. The reason the Norinco stuff blew out was because it wasn't seating fully in the chamber. Actually that's a pretty good indication of some though brass in that it bulged that far without blowing out. It would probably tell the tale if you took a mike to the Norinco cases and compared their diameter at neck, shoulder, midcase and base. I'll bet they're a bit larger.

[Rail Driver]

What's my answer?
The ammo is most likely the primary cause based on what you've reported.

The chicom stuff is MUCH tighter in the ar chamber... a few pieces were even snug in my glock chamber- and those are pretty sloppy.

So, i think the ammo may have contributed to the issue.... also did a web search on Norinco 9mm and found a few threads with people complaining about VERY hot loads and spotty specs.

by comparison, the WWB ammo dropped in MUCH smoother and "clicked" easily into the chamber... ^answer

[lowepg]

The ammo is most likely the primary cause based on what you've reported.

^answer

Ok thanks- just wanted to make sure I understood what you meant.

My plan is to get some KNS pins and rebuild the lower. Then go back and function test with reliable ammo.... Hopefully that gets it done....

[JT-AR-MG42]

You don't mention if the AR pistol has a ramped bolt or not.

Colt recognized this problem early on with all of the broken hammer pins.

Your gun and your choices, but I got the bolt ramped on mine to keep the holes in the soft alloy lower receiver from egging out under the stress of the unramped bolt.

Unramped bolts put too much stress on the hammer and both its pin and the pinhole by recocking the hammer much too fast during recoil. Pins will continue to be the weak item in an unramped system.

Might need to save the Norinco for something else. The AR blowback action allows the hammer forward to strike the firing pin AS the bolt goes home, not after anything has locked into battery as with a conventional locked breech 9mm handgun.
Lower the hammer by pulling the trigger - on an empty chamber - as you ease the bolt forward and you will understand the OOB with oversize ammo.

JT

[lowepg]

You don't mention if the AR pistol has a ramped bolt or not.

Colt recognized this problem early on with all of the broken hammer pins.

Your gun and your choices, but I got the bolt ramped on mine to keep the holes in the soft alloy lower receiver from egging out under the stress of the unramped bolt.

Unramped bolts put too much stress on the hammer and both its pin and the pinhole by recocking the hammer much too fast during recoil. Pins will continue to be the weak item in an unramped system.

JT

Bolt was ramped by DDLES.