03-23-2020, 05:24 PM
Klem Wrote:A5 has hit the nail on the head.
It's primer flow or cratering caused by lack of support around the pin. Basically the firing pin hole is too big for the pin. Flow happen with normal loads as well as hot. The next severe step is that small circle donuts start breaking off the primers and get in everywhere to jam the action.
A thicker, stronger primer will mitigate this. A tighter hole with better tolerances from a quality manufacturer will solve it.
This. I have been dogged by this with my 6.5 CM, with a batch of ammo using soft primers, where it would blow a punch of the primer brass back into the firing pin channel, and cause all kinds of problems. FWIW, they were S&B primers, and I no longer use S&B primers for 6.5 CM loads; as they are just too soft for the high pressures of 6.5 CM. And yet, they aren't strong enough for a small-firing pin indentation, and will pierce. Work fine in a lower pressure round with a fat round firing pin tip like an M1 Garand or 1903, but for a modern 6.5 CM, I can't make them work.
Though, I will say, I do have S&B factory ammo, and in my guns that seems to work OK, just the independent S&B primers in reloads are doing it to me.