Home Forums Hunting & Shooting Gunsmithing Win 70 piercing primers

A pierced primer is a primer which has been cut by the firing pin tip and leaked through the hole produced by this cutting. A primer blanks when the primer cup is insufficiently supported by the firing pin tip. Blanking occurs when the firing pin hole is too large, the firing pin mass is too low, the spring is too weak, the primer cup has been weakened by a poorly shaped firing pin tip, the primer cup is too soft or thin, or a cobination of two or more of these factors.
In blanking, the hole in the face of the bolt acts as a die and the gas pressure acts as a punch. The result is a nicely formed disc which is punched out and often driven back into the bolt body.
There is a fair amount of overlap with the two conditions so that damage caused by one may increase the likelyhood of the other. A primer may blank because the primer cup was too soft. The escaping gas may cut the firing pin tip which will cause it to pierce the primers later on. AQ poorly shaped pin may pierce the primer and the escaping gas might slam the striker back and collapse the mainspring. The weakened spring will offer insifficient support to the primer and blanking will result.
A rifle which blanks primers will usually give some warning in the form of cratered primers. The primer may crater due to a lack of support by the firing pin or because the primer cup has been weakened by the pin.
Generally, a rifle which is piercing primers can be cured by simply re-shaping the firing pin tip. A rifle which is blanking primers may repond to the same treatment if firing pin tip shape is a contributing factor.
Most of the rifle bolts I have ended up bushing were rifles which used small rifle primers and were loaded on the hot side (6BR's were common offenders). My own 30/06 was on of the few rifles I've had which blanked large rifle primers. Another which comes to mind was a Remington 700 300 Win Mag in which Remington had drilled the hole oversized. Most of the rifles I have bushed have been Model 70's (Post-64) and Remington 700s but I've also done a couple Rugers and some miscellaneous actions. I have never had to do a Mauser or an Enfield. Although the Mauser pin diameter is largish (technical term), the striker assembly is heavy and this mass helps to support the primer cup.
CAFR,
Sorry to have offended you but the things you mentioned , while worth looking out for in general, don't play much part in blanking or piercing of primers as far as cause and effect is concerned. An analogy might be- if the car won't stop, check the brakes. Tire pressure, while important to monitor, is not likely the culprit. I could, perhaps, have been a little more polite. GD

I think GD covered it. Some times when you blank a primer the little disc ends up going past the firing pin and into the bolt. It can cause a misfire as it can wedge between the pin and bolt body. This causes incomplete ignition. I've had the problem twice. One time was a weak firing pin spring and the other was on a rifle that had a .078 firing pin and excess clearance between the firing pin and the hole in the end of the bolt that it traveled through. Bushed the bolt nose, drilled and fitted a .0625 firing pin. Actually I just reduced the existing firing pin.
I've heard of a pierced firing pin, but have personally never seen one.

What is the process for bushing?

Basically, the bolt is drilled out to accept a flanged bushing which pressed into place. The bushing should be long enough to guide the pin. The flange about 1/8" thick.
For a Remington 700 in 223, for instance, the bushing will be .200 in diameter with the flange being .375 in diameter. In other words, the bushing replaces the entire bolt face with the flange sitting on a shoulder. I make the bushings of EN30B which is a high nickel, impact resistent alloy. Tough machining but finishes nicely. I use the same material if I am making a bolt head. Bushing is made .0005 over and pressed in and Loc-Tited.
I have threaded bolts for the bushing but this can be problematic as the bolts are occasionally just too hard to tap well so I went back to pressing them in.
This is just a general description of the process but I'm sure you get the idea. GD