LR308 pierced primers

[44junkie]

Greetings.

I recently made up a new batch of ammo for my LR308 and seem to be having a problem with pierced primers. Load is Nosler 168gr HPBT over 43.9gr Varget in a Remington case that's been trimmed, deburred and chamfered. Primers are Federal 210 and CCI 34. OAL is 2.810, about .050 short of contact with the rifling. Looking at available data, this is on the low end of things, so I'm puzzled.

Looking at the pic below, the shoulder of the primer is still well rounded, but the primer strike is just about pushed through the firing pin hole. About 1 in 10 actually pierced. There are no extraction problems. Headspace appears fine since fired cases are nominally .001 - .002 longer than before firing, measured at the shoulder with a RCBS case mic. 5 shot groups are a bit larger and less consistent than I used to get with this load, now running between 1 and 2 MOA. Chamber and bore are spotless. Sorry, no chrono.

Thoughts??

 

[rcmodel]

Pierced and leaking black soot?
Or extruded into the firing pin hole and not leaking?

Looks to me like you have a bolt with an oversize firing pin hole, coupled with a firing pin that doesn't fill the hole.

If leaking black soot, your firing pin tip may already be eroded and rough.
It will only get worse, not better, until you replace the firing pin with a new smooth one.

rc

 

[44junkie]

Yes, pierced and leaking. A wisp of smoke out of the action and the anvil hanging out of the hole in the primer.

I'll inspect/measure the firing pin as suggested. Hope it's as simple as that...

 

[44junkie]

Here's some pix of the bolt and firing pin. They seem OK to me. LMK what you think.

Also a pic of the pierced primer. Note the anvil hanging out with a firing pin divot in it.

 

[kingmt]

Second time this week I have heard this with Federal primers. The other was in a Glock & the primers showed no signs of pressure. I'm going to suggest you call Federal.

 

[StandingTall]

Maybe it's just my eyeballs, and maybe this has nothing to do with the problem, but the primers do appear to be seated a bit on the high side. Are you using a primer pocket uniformer during case prep?

BTW, those are some nice clear pics!

 

[44junkie]

@kingmt - Problem happens with Federal and CCI primers.

@StandingTall - Probably just the camera angle. Fired cases have primers flush with base. Unfired primers are seated just below flush.

 

[fguffey]

Pierced primers, again, I have never had a pierced primer that did not involve a weak firing pin spring, it is a .7854 thing. The spring must be able to prevent the firing pin from being pushed back by high pressure.

The firing pin crushes the primer, then the pressure inside the primer forms the primer to the protruding firing pin, it appears the bolt face has been cut by hot, high pressure metal cutting gas from the center of the primer, primers leaking between the primer pocket and primer normally leave a circle the diameter of the primer.

F. Guffey

 

[243winxb]

Pierced or Blanked Primers.

Pierced or Blanked Primers.

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1. Check the firing pin, it should have no gas cutting or deformities. 2. Firing pin protrusion should be checked. Internet search shows .055" to be about right for an AR15/223??. Check with a gun smith as each firearm is different. 3.The firing pin must stay in contact with the primer on firing. A weak hammer spring on an AR or a weak firing pin spring like on a Rem 700 bolt action will let the firing pin rebound on primer piercing when the hot gas pushes the pin backwards. 4.If the hole the pin sits in is to larger in diameter, the primer flowes back into this hole till the center of the primer separates and fall into the action or travels into the firing pin area. Bushing the firing pin hole will fix this. Or you may want to try a magnum primer with a thicker cup. Military ammo may have a crimp that needs to be removed before seating a new primer. The crimp is removed by reaming or swaging the primer pocket. Swaging may be needed here so the prime can be seated lower in the pocket. High primer = misfires & pierced primers. Varget-Variations between lots can produce different pressures, if you believe post on the web. Reduce you powder charge if all else fails.

 

[gamestalker]

Way back when I first started loading bottle neck cartridges I made some mistakes in how I worked my loads up, and I did in fact pierce a number of primers, CCI BR if memory serves me well. So my experience was 100% related to my loads going over sustainable pressure. I backed my powder charge down and have never had a repeat in close to 3 decades.

But I have to agree with others here who hold the FP, or the FP extrusion hole responsible in this particular case. Has this action ever pierced primers in the past, or is this the first batch that has caused issues? I ask because it's always a good idea to review all possible culprits, including pressures for safety sake.

 

[P-32]

AS I sat there reading this post I got to thinking, Dangerous I know, but maybe we are having problems with the CCI's now.

Not so long ago I chewed out a guy who was piercing CC primers for being over pressure. He claimed to be at a low pressure loading. I have never had a problem with CCI's but did with some small rifle Federal match primers. Since CCI and Federal are now owned by the same group as Remington, Marlin and a few others. It appears to me the new owners might be getting cheap on us and losing the once rock solid performance we all know. Just a thought.

I mean who ever would have thought a Marlin rifle built before a certain date is now worth more?

 

[kingmt]

I have a Rem 770(actually 2 of them) that crater the primers bad but haven't poped a primer yet. Weak spring is my next guess.

 

[44junkie]

Went to the range again today to try to sort this out. Tried some factory loads (WWB) in the LR308 and the primers pierced. Tried my reloads in my bolt rifle and there were no problems at all. At this point, I've ruled out ammo, which leaves the gun itself.

fguffey and 243winxb may have the answer I was looking for. About a year ago, I removed the crappy factory fire control group and dropped in a Timney trigger. I love the way it feels, but it could be that the hammer mass and/or spring are just too light to keep adequate contact between the FP and primer. I'll put the factory trigger back in and see if there's any improvement.