pierced primer question

[taliv]

i am in the middle of fireforming 400 pc of brand new lapua 260 brass to 260AI. for some reason i've had 2 pierced primers in the past 50 rounds. i can't remember the last pierced primer I've had, but it has been thousands of rounds ago, and never while fireforming.

42g of reloader 17 has been my load for years in both 260rem and for fireforming 260 brass to 260AI. my 260AI load is a full 3 grains more powder and sometimes 4 grains more. so i'm somewhat skeptical that the primer piercing is due to overpressure. the primers ruptured in the center, but are not flattened. there is no ejector mark. the web of the case is exactly the same diameter as it was prior to firing.

both came from the same tray of wolf primers, but it is the last tray in the box of 1000 with none of the other 900 pierced.

i'm going to back my ff load off another grain just in case, but if anyone has any ideas what to check, let me know.

oh, coincidentally, AJ just sent me his bighorn firing pin disassembly tool which arrived a couple days ago. So i took the opportunity to disassemble it and inspect it. It has close to 12,000 firings on it, but looks none the worse for wear. The tip is not sharp or eroded.

 

[Blue68f100]

I would take a close look at the FP. Failing where the FP hits can happens with excess clearance between the FP and hole. You normally want these as tight as possible so you don't get any primer flow to the gap. You said you inspected the FP did you feel any burrs or roughness? Is the FP doomed/rounded with no burrs.

 

[lauderdale]

I don't no how to put up address, but search" pin hole in primer" It's by GAHUNTER12 very long and very informative! Hope it helps.

 

[Walkalong]

Check firing pin fit to firing pin hole. Firing pin spring could be weak. Could be a couple of thin primers, or a combination.

 

[fguffey]

for some reason I've had 2 pierced primers in the past 50 rounds.

The two pierced primers are obvious, without knowing what the other 48 primers look like there is no way to determine what caused the holes.

Normally the firing pin dents the primer then the primer conforms to the shape of the firing pin, if the pressure inside the primer is greater than the springs ability to resist being compressed, a hole appears.

Problem, hot high pressure metal cutting gas escaping back through the punched hole can cut the firing pin and bolt face. When I form cases I form cases, there are times I find it necessary to fire form, when I fire form I do not use toilet paper, cereal or wax, I am not the fan of reduced loads.

F. Guffey

 

[243winxb]

Pierced or Blanked Primers.

The case has to much slop in the chamber when fire forming?

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. 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

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[taliv]

One thing that is interesting about this lapua brass is that the primer seems to seat further than with the hornady win and Rp brass I've been using.

I haven't measured it but it just feels deeper.

 

[fguffey]

What rifle/receiver? How did the chamber become an Ackley Unimproved chamber?

F. Guffey

 

[taliv]

http://precisionmultigun.com/pics/bighornsentinel4-14.jpg

bighorn action. i'm nearing the end of life on the 6th barrel, which was chambered by robert gradous. he used my 260AI reamer to cut the chamber. not sure what you are asking.


243x, hmm... you know, a couple of these cases are going in easy, where they would normally require a couple thou of crush. it didn't occur to me until i just reread your post.

 

[fguffey]

not sure what you are asking.

Not what but why.

which was chambered by robert gradous.

http://www.gradousrifles.com/

Seems a lot of guessing could have been avoided if the most important details were listed in the first question. The chamber was not cut in a barrel with an existing chamber. The Ackley Improved chamber is designed to fire form cases while the parent case head spaces on the neck/shoulder juncture of the new chamber. Part of the neck/shoulder is sized when chambered, meaning there is no loose, rattling, moving around case in the chamber, the case is held in by the face of the bolt and shoulder/ neck juncture.

The neck on the Ackley Improved chamber is longer than the neck of the parent chamber, meaning the parent case neck is sized when it hits the juncture.

But if it is as you say some of the cases fit and some do not it can not be caused by the chamber. The problem can only be caused by the length of the case from the shoulder to the case head. PROBLEM" You are using

400 pc of brand new lapua 260 brass

That eliminates a problem caused by the brass, unless you got a bad batch of brass.

F. Guffey

 

[taliv]

sorry i still have no idea what you're saying.

 

[fguffey]

243x, hmm... you know, a couple of these cases are going in easy, where they would normally require a couple thou of crush. it didn't occur to me until i just reread your post.
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It would appear you have all the information you need.

F. Guffey

 

[fguffey]

Taliv has solved his problem but on the outside chance there are others that have and or having this problem with a new custom rifle and new high end quality brass I suggest good habits and know your gun,

Guns, there is control feed and push feed. I eliminate bad habits, all of my ammo is feed from the magazine I do not care if it is push feed or control feed, but when someone ask me about my receiver I explain to them the difference between control feed and push feed and the problems that can be created when a control feed is treated like a push feed. As Taliv has decided the problem can not be the custom rifle by

http://www.gradousrifles.com/

and there can not be something wrong with his high end expensive cases, but on occasion some cases chamber with 'a crush' and some do not. Back to the remote possibility someone could experience pierced primers because the extractor is behind the case head and not in the extractor groove.

That would mean the firing pin struck the primer at the end of its travel, back to the lack of information, I do not know if Taliv is using toilet paper, wax or bullets when forming.

He should not be having trouble with cases that crush when chambered and cases that do not have felt resistance with a new custom gun and new high end expensive cases.

As you can read I can not help him, for others? I suggest feeding the rifle from the magazine.

F. Guffey

 

[taliv]

Actually I haven't solve the problem but I have fire formed another 100 cases with no further issue. I can't see how it could be related to the extractor. Fwiw the bighorn uses a savage-like sliding extractor.

My only guess as to an explanation is that I somehow screwed up neck turning those two and cut too deep into the shoulder which let them go farther forward and created enough headspace that the firing pin wasn't offering as much resistance as it needed.

I guess the fp spring might need replacement too but if that were the case I would see frequent issues. Not only 2 out of 250 cases so far. (I have 400 total to do by this weekend)

The problem with the turning the shoulder explanation is that I'm only touching maybe a mm from the neck. Not getting to the datum. Actually I think I just figured it out while typing. Since the 20* shoulder isn't fire formed yet when I stick it in there it can only headspace on the part adjacent to the neck which I'm cutting. So I guess I have figured it out now

 

[243winxb]

My Savage Axis 223 rem. firing pin strike will set the shoulder back .006" when measured from head to datum. A 2nd strike sets the shoulder back even more. I noticed this when looking for a reason why a round didnt fire. The primer fired on the 4th try. I wonder if its possible with a 260?

 

[spitballer]

For what it's worth it occurred to me that a deeply seated primer will be pushed back and wrapped around the firing pin, stretching the already thin metal more than a primer that is seated close to the bolt face. I could never understand this business of bottoming out the primer in the primer pocket. Nevertheless, an interesting discussion here...

 

[ironworkerwill]

I could never understand this business of bottoming out the primer in the primer pocket

If the firing pin has to push the primer all the way into the pocket and then just a little more to "set it off", that is time wasted and in theory accuracy lost. Some folks think of it as preloading the primer.

 

[taliv]

Spitballer the primer works better with a bit of compression and yes I'd energy is wasted pushing the primer deeper it may not go off

 

[243winxb]

Energy is wasted if the shoulder is pushed back also.

 

[fguffey]

My Savage Axis 223 rem. firing pin strike will set the shoulder back .006" when measured from head to datum. A 2nd strike sets the shoulder back even more. I noticed this when looking for a reason why a round didn't fire. The primer fired on the 4th try. I wonder if its possible with a 260?
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I got a call, seems a shooter was having trouble with his new rifle and new R-P ammo. He purchased 2 boxes of 30/06 R-P ammo, out of one box 5 failed to fire. the question to me was “What do you know about Remington ammo quality”, my answer “Their phone number is on the box", if there is a problem they need to know”. Instead of calling the 15 cases that fired and the 5 that failed to fire came over that afternoon. The 5 that failed to fire were chambered in three different rifles and hit with firing pins 5 times total. I make chamber gages, I have cut-off barrels and I have Wilson case gages and I make datum based gages. I was very impressed with the 5 cases that failed to fire, all the cases measured to minimum length from the datum to the case head. The fired cases chambered into my chamber gage and cut off barrel, meaning I could have neck sized them and used them in any 30/06 chambered rifle I have.

Because of the concern by the very disciplined shooter/reloader/builder that brought the cases over we tore the failed to fire cases down, again. I was impressed. we weighed the cases, powder and bullets. There was not 1/2 grain difference in weight between the components. We removed the primers, they had dents. We installed the primers back into the cases they were removed from,THEN! we chambered the 5 failed to fire cases into one of my M1917 rifles, the ones with the killer firing pins, after chambering the case, no bullet/no powder, I pulled the trigger. One by one they all fired without primer protrusion and the case did not shorten between the datum/shoulder and the head of the case.

Point? When someone tells me the firing pin strike shortens the length of the case from the shoulder to the head of the case I always ask: How do you measure that? Because I want to know what minimum length is I measure before firing, when I want to know the effect the chamber has on a case when fired I measure before then again after firing. Then there is the primer, I would think someone is using dent resistant primers if the case is shortening between the shoulder and case head upon impact, or there is a problem with keeping up with the sequence of events between pulling the trigger and the bullet leaving the barrel.

F. Guffey

 

[spitballer]

Egads, ironworker I think you're right. And all this time I thought that flush mounted primers never moved. This means that they're being thrashed about like pistons and actually more likely to rupture.

Interesting thread.