AR 15 blown primer

[hps1]

My grandson was shooting some RORC 5.56mm L2A2 NATO ammo in his Bushmaster AR 15 yesterday when he experienced a blown primer. Did not discover the blown primer until we were policing the brass after he had finished firing.

On checking other cases fired, most had a shiny spot wiped on the head of the cases, likely from the ejector.

I haven't had much AR experience, but the older gas guns (M1 & M14) were pretty hard on brass, too, but I can't remember ejectors marking the case head. As I recall, the extractor did a number on the case rim.

The blown primer is definitely a sign of high pressure (or excessive headspace for that particular round). Does the AR usually leave the ejector mark on rounds loaded to normal pressures or should it be considered a pressure sign, as it would be in other rifles? Anyone else have any problems with the surplus RORC ammo? Either way, will not fire remaining RORC ammo.

Regards,
hps

 

[Doug b]

Yep sure sounds like excess pressure.That bright shiny spot is from brass flowing into the ejector then being sheared off by bolt rotation.You might want to remove and clean the ejector. I highly recommend using the sinclair ar 15 bolt vise. www.sinclairintl.com

 

[Bartholomew Roberts]

I second the high pressure diagnosis. Now the question is whether it is the gun or the ammo.

 

[Doug b]

Bushmaster is top shelf, I would tend to suspect the ammo.Probably a reason it is surplus.

 

[mec]

I found a blown/completely de-primed case among the ones ejected from my bushmaster. I'm not really sure it came from my gun but I was shooting the federal LC 60 grain ball load and it was of that headstamp. I haven't had that problem with any other ammunition in this rifle.

 

[taliv]

my guess it's a combination of 223 chamber and 5.56 ammo

 

[Bartholomew Roberts]

Most of the Bushmaster line has a 5.56mm chamber or I would guess the same thing... the rifle wasn't a Varminter, match barrel or Predator was it? I believe the Predator has a Wylde chamber, so it shouldn't be an issue there either; but it would be tighter.

 

[hps1]

the rifle wasn't a Varminter, match barrel or Predator was it?

Yes it is a match grade Bushmaster; the DCM model IIRC.

Regards,
hps

 

[taliv]

there ya go

 

[hps1]

Looks like problem solved. This brings up another question or three. What about the Federal American Eagle ammo some have recently reported using LC brass? Is it 5.56mm or 223?

What is the difference in the two cases? I would assume either longer or thicker case neck on the 5.56mm?????

What about reloading 5.56 mm brass for use in the 223 chamber?

Thanks,
hps

 

[mec]

the Lc and federal and winchester brass I've weighed is about the same while the s&B I've used for a couple of loads is five grains heavier. these are upper end loads and nothing unusual occurs. I suspect that this brass has somewhal less capacity than the Lc etc.

 

[mc223]

The chamber is not the issue. whether it is a Wylde or a Bushmaster 5.56. Either of these chamberings will readily fire the RORC surplus ammo.
The blown primer is the result of the Inconsistancies of the ammo. A slightly reduced case capacity and a slightly heavier powder charge and a lighter primer swage would likely be the culprit. Being a military round they are probably loaded right at max. The RORC is not bad ammo, just not that good.

Don't assume that because a manufacturer uses LC brass that it might be dangerous. Federal's parent Corporation (ATK) Also is now operating the Lake City Ammunition Plant.

I load all of my own ammo for my Bushmaster, and have experienced a couple blown primers. These occured in load devolopment using surplus powders. Just a bit too warm.

 

[taliv]

yeah, that's why the ammo-oracle answers the question thusly:

Q. How can I tell if a round is SAAMI, US military, or 5.56 NATO Mil-Spec?
...
Generally you don't have to worry unless you're using a .223-chambered rifle, but it's a good idea to check regardless. Of course, if you have a Mil-Spec chamber, you needn't bother.

 

[Bartholomew Roberts]

The chamber is not the issue. whether it is a Wylde or a Bushmaster 5.56. Either of these chamberings will readily fire the RORC surplus ammo.

Except the Bushmaster DCM uses a .223 SAAMI match chamber instead of either of the chambers you mention. So you'll occasionally see some signs of overpressure with military ammo.

 

[hps1]

Thanks, guys. Looks like the problem is the GI ammo, being loaded to near max. pressures, fired in the 223 chamber is the culprit.

Regards,
hps

 

[Grump]

What??? nobody speculates that perhaps the brass itself is a bit soft?

AFIAC, primer crimp ain't gonna make any difference unless the primer pockets are already getting stretched. Whether by high pressure, soft brass, or both, I don't consider that a very safe situation.