The old nickel plated WLR was an excellent primer. That is what I used after two Garand slamfires with Federals.
Around 1999 Winchester changed their primers by eliminating the “nickel” finish to a “brass” finish. Back then I called Winchester to find out what that change meant for primer sensititivity. Per telephone conversation with Mr. Chris Huseman at Winchester Group, Olin Corporation the old WLR primer had a zinc plating on the cup. Mr. Huseman said the material was zinc, even though I thought it was nickel. Anyway, Winchester removed that plating, with other changes, to make their primers more sensitive. I was informed that the product change was specifically targeted to “combat light firing pin hits and off center strikes.”
Those were not words I wanted to hear. I did purchase 5000 of the brass WLR and used them up. Mostly bolt gun loads, but some gas gun loads. They shot fine, and I have not had a problem. But since slamfires due to overly sensitive primers are one in a million events, I would not automatically expect a slamfire to happen unless I had a serious mechanical problem.
I have heard of one WLR slamfire in a Garand on THR. The description was not conclusive one way or another in assigning a cause.
As for factory ammo, you are shooting the least likely stuff to cause problems. Factory ammo is so much smaller than reloads. The bolt is going to turn into battery without any resistance. This is great. Yes the firing pin is tapping on the primer, but there is no delay to bolt closure. So if there is a slamfire, the round will simply discharge, similiar to a mechanical malfunction. The gun will go boom, but not Kaboom.
Reloads cause 99 % of slamfires. Most people's size their reloads with standard sizing dies, folks don't set up their dies with a cartridge headspace gage, so their rounds are often too fat or too long, or both. This combination of issues creates an interference fit in the chamber. High primers can also cause problems. These things contribute to the probability of a slamfire.
And, as stated before, always feed rounds from the magazine.
I have a supply of CCI #200Large Rifle primers. Are these ok for my M1A?
CCI 200 primers have thick cups. That is good. Better than the brass finish WLR. Never tried Remington. Never ever use Federal.
