Bulged casings from new AR15

[kwelz]

I have a brand new AR15 and I started breaking it in today. It appears that the casings are bulged near the base. Here is an image. Any ideas?

Oh and here is the nice shiney new M4

 

[Stevie-Ray]

That's the one I want. What did you have to pay, if I may be so nosy?

Sorry, I don't know what the problem would be, besides a chamber issue or ill-loaded ammo? Is the ammo surplus?

 

[kwelz]

Headstamp: R-P .223 Rem
The same stuff I am sure most of us use. I prefer it for break in. Culd be a bad round. However after I saw it I decided to hold off any more shooting till I got a second opinion.

Paid 850 for it in Box. Marked LE only too

 

[ocabj]

That looks like a really loose chamber. Did you buy it as a complete rifle or did you piece it together?

 

[kwelz]

Nib DPMS

 

[rbernie]

When a chamber is a bit on the big side, the cases will bulge ABOVE the head - not in the head itself. Given this, I don't think that it's chamber sizing problem. The only times I've ever seen a bulged case head was when the round was REALLY REALLY overpressure and/or when case extraction began before the pressures dropped to a safe level. In this case, I suspect that the timing/pressures are a bit off.

I would NOT shoot any more of that ammo lot. Try another lot/brand and see what happens. I suspect that you'l find the symptom goes away.

 

[N.M. Edmands]

Check headspace.

 

[Bartholomew Roberts]

Check the headspace. Also consider checking the chamber dimensions to insure they are correct. Finally, try another brand of ammo; but I am thinking you have a problem with your barrel.

 

[kaferhaus]

Classic example of excessive headspace.... an overpressure round would have blown the primer out too. Normal pressure round in a oversize chamber (excessive headspace) will cause this problem without the corresponding blown primer.

 

[PMDW]

Nib DPMS

I think I found the problem.

 

[NMshooter]

Wow!

Never seen headspace that excessive...

Get it checked.

 

[kwelz]

Called DPMS. They are going to replace the barrel. Easy to deal with and very friendly.
Honestly the only people I see complain about DPMS are the Colt/Bushmaster/Armalite Fans on the internet. Everyone around here who has one seems to love it and while this is my first complete DPMS I have always been very happy with thier uppers before.

 

[rbernie]

Classic example of excessive headspace.... an overpressure round would have blown the primer out too. Normal pressure round in a oversize chamber (excessive headspace) will cause this problem without the corresponding blown primer.

Yeah, I didn't think that one all the way thru.

Having said that, I've never seen headpsace THAT bad. In the past when I've seen this, it was always a case of premature unlocking in a semi-auto. Given the AR reference, I presumed that it was a mismatch between the ammo and gas system and recoil system.

 

[Gewehr98]

There's excessive headspace...

And then there are oversized chambers. Don't confuse the two. You can have a chamber cut that's properly headspaced, boltface to shoulder datum point, but still very much oversize in case diameter dimensions, which is NOT a headspace issue. Chambering reamers that wobble and don't stay concentric to the bore can do that. Without an unfired round for comparison, it's hard to tell whether the shoulder was bumped forward any on that particular piece of brass. Bulged above the case head, yes, but what else is going on in there? Good to know DPMS will make the necessary changes, though.

 

[redneck2]

Fwiw...

I have a friend that shoots a lot of High Power. Had a friend with an AR that was pulling the heads off cases. Called RRA. Their first question was "are you using Remington cases?"

I'd maybe try ONE round of military or Winchester ammo and check over the case real well. Be real interested in your findings as I'm picking up my AR in a few weeks.

 

[kwelz]

Forgot to mention that I tried a few rounds of SS109 and had the same problem. THe bulge is just over 1/10th of an inch. The general concensus from DPMS and at Keislers is that it is an oversized chamber and not a headspace issue.

 

[rbernie]

Well, color me confused. I'm at a loss to understand how an oversized chamber can cause a bulge only above the head and not display a relatively linear taper up the case towards the shoulder.

Somebody edumacate me...

 

[N.M. Edmands]

Rbernie,re: " confused "- me too.
Azizza, were DPMS and Kieslers able to see your pictures? Please keep us posted, inquiring minds-------

 

[kwelz]

DPMS has not seen it however shell casings were included with the rifle. A couple people at Keislers have seen the shell casings. I don't know enough to be sure one way or another.

 

[DnPRK]

Poorly reamed chamber (oversize) likely due to bad setup by the machinist.

 

[PMDW]

Poorly reamed chamber (oversize) likely due to bad setup by the machinist.

I believe most quality firearms nowadays are made via CNC. But then, it is DPMS. I don't know how they do it.

 

[rbernie]

Poorly reamed chamber (oversize) likely due to bad setup by the machinist.

How so? I would expect that a wobble in the reamer would introduce a taper into the blown-out section, but that's not apparent in the pics.

I wonder if the chamber was cut too shallow and the barrel not screwed in as far to compensate and correct the headspace. That would theoretically allow the case to be unsupported just above the head. But I admit that I'm talking out of my a$$ here, since (at a minimum) I don't really know how the AR barrel is screwed into the receiver....

 

[Tweak]

Usually, that is caused by too great a radius on the lip of the chamber.

the barrel on an AR is not screwed into the receiver.

 

[kwelz]

The rifle came back today. THey put a new Barrel on it and Test fired the Rifle. When I got it home I tested it out and everything is perfect. Kudos to DPMS for the really fast turn around.