I load black powder cartridges for an antique rifle. I usually use magnum LR primers (regular primers are hard to find here, and there doesn't seem to be any pressure issues with a magnum primer). I decided to try LP primers, but most of the few (less than 4) that I shot ended up with pierced primers. Obviously I'm not going to shoot them anymore, but what would be causing this? The higher pressure magnum LR primers don't show any signs of over pressure. Are they just build stronger or something?