Yeah, slamming isn't good for seating primers, which is why I don't use the priming "system" with Lee Loaders anymore, even when I use the loaders themselves. Had a Large Rifle primer go off when I was 13 when using the Lee Loader for my Mosin-Nagant, and never wanted it to happen again. And it hasn't!

“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.”
John Steinbeck