unusually deep firing pin strikes

[Dux-R-Us]

Model 70 Winchester XTR. .270 Win. 3/20 empty cases showed deep primer impressions. The rifle had not been shot in 6 or 7 years. I do not know if the deep primer strikes were the first rounds fired or not, but they did occur in the first 10. Ammunition were hand loads. I am guessing that this is probably not much to worry about if this no longer occurs. Any suggestions as to the possible cause would be helpful. Thanks.

 

[Preacher]

Does the case on the right have a hole completely through the primer ??

 

[CatShooter]

Model 70 Winchester XTR. .270 Win. 3/20 empty cases showed deep primer impressions. The rifle had not been shot in 6 or 7 years. I do not know if the deep primer strikes were the first rounds fired or not, but they did occur in the first 10. Ammunition were hand loads. I am guessing that this is probably not much to worry about if this no longer occurs. Any suggestions as to the possible cause would be helpful. Thanks.

That is not a deep primer strike - you blew out a disk of metal from the primer cup.... look for the pieces to be inside of the bolt body.

 

[JORTZ]

That is a sign of over pressure for those primers

 

[CatShooter]

That is a sign of over pressure for those primers

While the other case shows a slight sign of pressure, punched primers are a sign of a weak firing pin spring.

 

[Nutjob]

I believe that is what they call a "blanked" primer. I'd disassemble the bolt and clean everything really well and try it again. You may need a new firing pin spring if the cleaning doesn't work. Also, when your bolt is apart check to see that the end of your firing pin is still nice and rounded. If it isn't, take a little emery cloth to it just to knock off the rough edges. Good luck.

Russ

 

[Utah338]

Weak spring or a wore firing pin. I've seen people think the firing pin was too long when a primer pierced so the filed on the pin to shorten it thus making it worse.

 

[DCRYDER]

I've also had this happen because of primer pockets were too deep.

 

[watercam]

I have had this happen when using small rifle primer .308 brass and a conventional (large diameter) firing pin. In fact it was a Winchester push-feed action/Speed-Lock firing pin and spring. Blanked roughly 10% of the primers in a string of 70 shots (firing pin finally locked up because of all the bits and pieces inside the bolt body). Shortened the firing pin to .035" protrusion and switched to primers with thicker cups (CCI BR4s from Fed. 205Ms). Still had a smaller percentage of piercings. In the end went back to factory (heavy) firing pin and spring - no more issues, rifle shoots great at 1000 yds. Simply did not want to have the firing pin reduced and bushed.
Curious as to the theory of how a weak spring causes this phenomenon. Seems counter-intuitive but I am open to new ideas!

 

[CatShooter]

Curious as to the theory of how a weak spring causes this phenomenon. Seems counter-intuitive but I am open to new ideas!

Not a theory.

The firing pin is what holds the pressure at the back end of the case.

The primer cup is a thin piece of metal (0.020", to 0.025") with ~55,000 psi of pressure trying to push it out - the pin is holding it back - if the spring is weak, the pressure pushes the metal into the bolt body.

The metal is not pushed into the primer by the pin, it is pushed into the bolt by the pressure.

Firing pin extrusion should be 0.050" to 0.065". Making it less does NOT solve the problem... it adds another problem.

 

[treeman]

if you have a standard 24# stricker spring and put all 24 lbs on a .070 dia. circle how many psi. would that be pushing against the primer? I don't know the mathematical formula to figure but it would be quite a few #/sq. in.

 

[CatShooter]

if you have a standard 24# stricker spring and put all 24 lbs on a .070 dia. circle how many psi. would that be pushing against the primer? I don't know the mathematical formula to figure but it would be quite a few #/sq. in.

6236 PSI (but it is 4:45 AM and I haven't had coffee).

So it is not enough on it's own - it also relies greatly on the strength of the metal in the cup, plus the dome shape of the pin tip to hold the pressure at bay.

I had perforated primers in one of my bench rifles. I went to a 28 pound spring and now I will get ejector marks on the head, but no cratering.

 

[KMart]

How long ago was the ammuniton loaded? What weight bullet, how much and what kind of powder, etc?

I had something similar a few years ago when I loaded a 270 with some of the old surplus 4831 that was sold back in the 60's. For 2 years, the load shot fine. The third year it gave ejector marks and some blanked primers. Upon pulling the bullets, I found corrosion on the bullet bases and a bad smell. I guess the powder finally went bad.

 

[CatShooter]

How long ago was the ammuniton loaded? What weight bullet, how much and what kind of powder, etc?

I had something similar a few years ago when I loaded a 270 with some of the old surplus 4831 that was sold back in the 60's. For 2 years, the load shot fine. The third year it gave ejector marks and some blanked primers. Upon pulling the bullets, I found corrosion on the bullet bases and a bad smell. I guess the powder finally went bad.

What was the bad smell??

 

[KMart]

A sharp acidic smell

 

[BoydAllen]

The first thing that I would do is to replace the firing pin spring, and check the tip of the pin under magnification to see if it has been flame cut by the primer failure. If it has been, smooth the surface with a stone, spinning the pin in a drill. Do not extend the radius down the pin any farther as this will contribute to cratering. I prefer not to use a hemispherical tip contour but one that is flatter in the middle, with a smaller radius at the sides. If the hole is oversized for the pin, that can be a contributing factor. If you want that fixed, Greg Tannel of Gre-Tan rifles does a fine job, with a fast turnaround for a very fair price.

 

[s100whunter]

I too had this happen same thing old ammo and they were not reloads bad smell and corosion on bullets

 

[Dux-R-Us]

That is a sign of over pressure for those primers

While the other case shows a slight sign of pressure, punched primers are a sign of a weak firing pin spring.

what specifically is it about the left case that shows sign of excess pressure?

Thanks to all responders. I've sent my rifle off to Greg Tannel for bolt and trigger work.

 

[fredhorace77]

somewhat flat primer edges