Primer piercing causes

[Laurie]

If your SPR was made well before they got the word that FN was closing the CT factory then it was "special" but the one I had was definitely NOT.

I was probably lucky there. Mine was one of the first 10 imported into the UK, and very early production. (In fact, not many made it here in total, not helped by an importer who took over doubling the price believing it to be a truly special rifle.)

The only thing wrong with mine (fat firing pin aside) was it was very picky over bullet weights and loads making it difficult to find 'sweet spots'. That was with a Bartlein Heavy Palma barrel in 260 Rem. I came to the conclusion it was a bedding issue in the McMillan A4 synthetic stock. Certainly, the Sniper's Hide Forum had lots of posts on pillar-bedding these beasts suggesting there was a problem.

 

[243winxb]

Can someone comment on why the pieced primers have the metal pushed into the hole. You would think 55,000 PSI would push outward?

The tiny piece of primer metal is blown towards the firing pin. The piece may enter the pin channel or just get lost in the action.
The pierced primer is caused by high pressure, excessive head clearance or a defective primer.

The firing pin strike can set a 223 shoulder back .006" using a claw type extractor.

The firing of the primer alone, no powder, produces about 23,000 PSI in the pocket.
Hammer bounce is a known occurrence in revolvers. Double firing pin strike.
I think it happens also with bold guns.

The primer would seem to back out of the pocket, on firing, then be reseated. Many rounds fired, leave a ring around the pin hole, on the bolt face.

 

[243winxb]

The primer manufacturers have the cup material cold rolled to a specified hardness

Some cups get annealed. May help stop gas leackage, on firing.
https://winchestermilitary.com/Primers

 

[Hengehold]

The firing pin diameter in this rifle is .068”.

Does this fit into the small-pin or large-pin category?

Also, the pin is .068” and pin hole is .070” so excessive clearance is not the issue.

 

[LCazador]

The firing pin diameter in this rifle is .068”.

Does this fit into the small-pin or large-pin category?

Also, the pin is .068” and pin hole is .070” so excessive clearance is not the issue.

That is correct size firing pin size for small-pin and .378" bolt face. I think you're load is too hot as the VV website lists 22.8 grains of N150 as max load. If you're seating into the lands that will drive the pressure even higher. Did you measure head diameter after firing? How much expansion?

 

[jelenko]

Remember, OP's freebore is .195.

GRT using a Wylde chamber, his observed velocity, case size and barrel length shows a max pressure of 55K.
With a longer freebore the pressure would be less.

 

[Hengehold]

That is correct size firing pin size for small-pin and .378" bolt face. I think your load is too hot as the VV website lists 22.8 grains of N150 as max load. If you're seating into the lands that will drive the pressure even higher. Did you measure head diameter after firing? How much expansion?

Good points.
The load in question is jumping .020”

 

[Walt Krafft]

My bolt is nitride coated so I will have to call Pierce to see if bushing the firing pin is even possible.

It is.

 

[DaveTooley]

Can someone comment on why the pieced primers have the metal pushed into the hole. You would think 55,000 PSI would push outward? I guess the cup slams against the bolt face, does the gas then push the FP backward compressing the spring then it hits twice?

There's been many Jewell triggers broken by blanked primers. The firing pin gets slammed to the rear by the pressure on the disc.

 

[Hengehold]

Thank you to all who have posted here and shared your experiences. Through the process of elimination I think we have narrowed it down to pressure as the most likely candidate based on the below findings. Please let me know if I am off base on any of them.

1. Firing pin is not oversized. It is currently .068”. Am I wrong about this firing pin being small enough?

2. No excessive space around firing pin. Firing pin hole is .070, pin is .068. Total of .002” clearance.

3. 205M Primer should be adequate for this application. There are thicker primers, but 205M should be sufficient.

4. Additional pressure signs are not present. Have not been able to measure stretch above rim recess between once fired and twice fired case so this is still an unknown.

5. Theoretical chamber pressure with the .195 freebore should be mid-50k PSI.

Conclusion: the most likely causal factor based on these facts appears to be pressure. Will have to reduce power charge.

 

[dellet]

40 rounds at 70 degrees no problem. 4/25 at 40 degrees have a problem. It would be real rare for powder to be the issue, it actually should have been lower pressure than ,the day before. Carbon and lube certainly create more problems cold than hot.

Any chance the firing pin was hanging up, not retracting?
Compressed loads, sitting over night and pushing the bullet out?

 

[jelenko]

GRT puts the load with MV at 2790 in the mid 50K. And Laurie thought it would be fine.

 

[M-61]

Why are you bumping 0.002? Or should ask why are you bumping?

That is the first question! Why?

 

[Hengehold]

40 rounds at 70 degrees no problem. 4/25 at 40 degrees have a problem. It would be real rare for powder to be the issue, it actually should have been lower pressure than ,the day before. Carbon and lube certainly create more problems cold than hot.

Any chance the firing pin was hanging up, not retracting?
Compressed loads, sitting over night and pushing the bullet out?

I agree, pressure should have been lower in the cold weather and pressure seems to be unlikely given the circumstances. However, it seems like we have ruled out the firing pin.

1. The rifle is brand new, so there is no buildup of junk in the pin hole or bolt body to obstruct pin movement. I suppose I will have to send the bolt back to Pierce for inspection. Maybe something is out of spec?

2. The load does not appear to be compressed to me. Powder is below neck shoulder junction and bullet’s boat tail junction is only about halfway down the neck, so there is room for the boat tail without displacing much powder. Also, I don’t notice any crunching powder when seating them.

 

[Hengehold]

That is the first question! Why?

I am FL sizing brass. Common practice is to bump shoulders back .002-.003” in order to allow fired brass to fit into chamber without interference and leave a little room in case debris makes its way into chamber.

Are you implying that I should be neck sizing or something else?

 

[Hengehold]

GRT puts the load with MV at 2790 in the mid 50K. And Laurie thought it would be fine.

Agreed. Seems like excess pressure should be unlikely but we have ruled out the other possibilities. Which only leaves pressure as the remaining variable.

 

[M-61]

I am FL sizing brass. Common practice is to bump shoulders back .002-.003” in order to allow fired brass to fit into chamber without interference and leave a little room in case debris makes its way into chamber.

Are you implying that I should be neck sizing or something else?

Not at all. Shoulder bumping in my opinion, is done to correct a case that does not chamber ( bolt close normally). Not as you say is a ‘common practice’. I am referring to bolt actions rimless cases. 2-3 thousandths is increasing headspace in addition to the existing headspace. If a case has stretched to the point the bolt doesn’t close it is necessary to bump the shoulder back, and not an arbitrary number.
The greater the headspace the more the cases stretches when fired. That will happen X number of times until the case separates. For me bumping is not a step in reloading rather something that is done to a case to correct a problem. Some cartridges are notorious for stretching while other ( like a 222) don’t seem to stretch at all.
As far as debris in the chamber there should ideally be none. However everything I’m stating is shooting from a bench rest. Not hunting.
I attempted not to be confusing.
There is a lot things happening when you pull the trigger aside from the bullet exiting the barrel.