Pierced primer
 

I have a Parker hammer gun that I have shot many times but on two or three occasions I found the spent shell's primers had a hole in them as I extracted them.

What would cause a primer to be pierced AND what are the effects and dangers? Is it the shells or the gun?

It's the gun or primers. Some claim the Chedditte primers will do that. Or, one of your firing pins are a bit too long or too pointed. I see it off and on and don't think there's any danger.

I agree with Paul. I have only seen this happen with Cheddite primers. That isn't to say it couldn't happen with other brands. Rob, Check the nose of the firing pins. Sometimes just stoning and polishing them a bit solves the problem.

Isn't the pierced hole a route for blowback? (Make sure you're wearing your glasses)

I get pierced primers - any brand - mostly with hammer guns that have strong main springs and longer than most firing pins. I think that primers used to be a fair bit thicker and tougher. I get a bit of blowback and am careful to clean the firing pins.

If you're using your own reloads, try seating your primers a little deeper in the base of the shell if you have an adjustable seating depth reloader. You'll be moving the primer further away from the "too long" firing hammer or pin. Of course, when you start using a primer with a thicker primer cup body, you will not have the striker force sufficient to get good ignition (maybe).

Bindle:
Firing pin tips should be hemispherical and protrude no further than .050 from the breech face. With this correct and good primers, the problem should go away. But... every pierced primer allows gas and carbon back into the action and stock cuts. Too much is never good for either.

Best, Kensal

Kensal, Is .050 for all types of firing pins, straight and the offset pins. Gary

Gary:
As a general rule, yes. Many are a tad shorter and work just fine though.

Best, Kensal

I am still in shock and mourning; a pierced Cheddite Primer and associated blowback blew apart the head of my Parker VHE stock this morning. Shell was a reload (mine) and can't help but think it was my own error, but I can't see anything wrong with the spent casing other than the primer is pierced, although perhaps the hull is expanded slightly more than other cases. Case looks clean with no signs of excess pressure, primer was fully seated, crimp looked normal, etc. All I know is that my beautiful 1929 gun is in sad shape. Sign.