pierced primers, factory ammo

[rpoL98]

My Aero AR-10 in 308 is experiencing some pierced primers, with factory ammo, not handloads. MAGTECH 308 168gr HPBT.

I did check the headspace with GO, NO-GO gauges at assembly and it checked out good. It's got an Aero NIB bolt, and using wire-size drills as gauges, the firing pin hole checks out at 0.081", and the tip of the firing pin is about .0780". It's killed 1 firing pin already. Is it the ammo? "thin primer cup"?

I examined the tip of the replacement firing pin, and it's got a nice radius to it, still smooth, but I already had another pierced primer with the replacement FP. The primer is still in the brass, it's just got a hole in it.

Also have a Geissele HS-NM trigger in it. 24" Brownells/Satern barrel. I didn't have this occur at all when I was shooting M80 ball ammo.

I noticed that in comparison, my Aero nitride 308 BCG has the high-pressure version firing pin & bolt, I think that's what it's called, nominal .070" aperture, .067" firing pin tip. Wondering if I should switch out the bolt to this HP version. I would like my firing pin to last more than 1 box of ammo.

 

[bfoosh006]

I'd swap and give it a try. Fire a single round and check , thoroughly for any irregularities.

For safeties sake .. go/ nogo gauge it prior to firing.

It is possible the bullet is jamming into the lands.

Or thin primer cups... or excessive FP protrusion.

Have you tried any other factory ammo ?

 

[rpoL98]

I'd swap and give it a try. Fire a single round and check , thoroughly for any irregularities.

For safeties sake .. go/ nogo gauge it prior to firing.

It is possible the bullet is jamming into the lands.

Or thin primer cups... or excessive FP protrusion.

Have you tried any other factory ammo ?

if I swap bolts, I'll be checking the headspace, for sure.
I've shot quite a bit of MAGTECH 147gr M80 FMJ, and also PMC Bronze 147gr FMJ, no issues.

I'll look into the other aspects, thanks.

 

[rcmigpilot]

Had the exact same issue with Prvi .223 69gr match in my bolt gun, I would get at least one pierced primer per box. At first I thought it was the firing pin in the bolt gun so I shot some through my AR and got the same results. Did a little research and other people have had the same issue the Prvi match loads, maybe Magtech is getting some of the same soft or thin primers.

 

[hermosabeach]

HSM had a batch of 50 BMG back in 2004 or so that had a similar issue... primers would puncture and the jet of gasses would mess up your bolt.

If you have unfired ammo, can you take a pic of the primers? Are they seated too far out?

Can you pull a bullet from a loaded round and fire a primed case to see if the primer is punctured when fired? (ear pro is needed if you do this in a garage)


Trying to see if it is ammo or your hardware

 

[DavidAR10]

Throw the ammo into a case gage to check shoulder.

 

[Snuby642]

My son has fired well over 1000 rounds of that same ammo in his ruger.
Have not seen any problems.
Every manufacturer has a bad day.
Since you have changed firing pins the bolt would be suspect as to having too much pin protruding. The primers look penatrated very deeply to me.

Imho that is very deep.

Edit] since no problems with other ammo like @rcmigpilot said bad primers may be a better case.
Would not hurt to contact mag tech with lot #.

The factory mag tech rounds have been about 7-8 thousands below our chamber unfired and consistant but a bad primer batch would be hard to qc.

 

[black max]

The ammo is obviously to hot for your rifle, stop shooting it!

 

[rpoL98]

Throw the ammo into a case gage to check shoulder.

I don't have a case gage (yet), but that will be on my next Brownells order. I thought I had one, but couldn't find it, checked my records of purchases, nope, never bought that one. I'll set the box of ammo aside for now. BTW, primers are flush.

labeled as:
.308 WIN
10,89g (168gr) HPBT (308D)
BV0327 L-0830

I have some more boxes from that same case, will try some from there with my replacement HP bolt, I did check the replacement bolt headspace, it's good. Will measure the FP protrusion when I strip it to clean it, along with the original bolt FP protrusion.

 

[clcustom1911]

PM inbound

 

[kenny1773]

My AR10 does not like S&B 140gr 6.5 creedmoor. I had primers completly blown out of the brass case and flying all over
My gun also passed go - nogo check with flying colors and never had a problem with hornady

Magtech owns S&B, so I imagine there might be something to that...

 

[Herstal 12]

Try different ammo before replacing parts on your rifle and narrow down the source of the problem
Cheers

 

[bfoosh006]

My AR10 does not like S&B 140gr 6.5 creedmoor. I had primers completly blown out of the brass case and flying all over
My gun also passed go - nogo check with flying colors and never had a problem with hornady

Magtech owns S&B, so I imagine there might be something to that...

Those S&B 140gr FMJ factory rounds might be jamming into your barrels lands... the ogive is very different then the Hornady bullets.

I suggest you permanent marker the whole exposed bullet and see if it is hitting the lands when chambered.

 

[bfoosh006]

Interesting the case head pics don't show typical over pressure signs... ejector smear, and harsh extractor claw abused case rims.

Maybe your batch of CBC ammo has thin primer cups.

Or like speculated, your FP protrusion is excessive.

 

[rpoL98]

Firing pin protrusion on the original Aero 308 bolt is .040". not sure what the spec is...
Firing pin protrusion on the replacement HP bolt with the skinny FP is surprisingly .045". Replacement bolt is from Rubber City Armory.
I didn't have any more pierced primers with the replacement HP bolt, using ammo from the same case, same ID numbers on the boxes. I'll probably leave the HP bolt in the bolt carrier for this upper, although at this point, I'm guessing some defective primers were in that batch.