Its probably your reloads. Do you plunk test or have a chamber gauge? the other obvious thing would be primers that are not fully seated. They should actually be slightly below flush with the bottom of your brass. At lot of guys don't trim their brass or clean out the primer pockets, which is fine if you want to make quick blasting ammo but the more steps and final QC you skip, the more problems you will have.

It can happen to anyone, I had a couple 45acp round that just would not fire in my 1955, I ran the couple I had through 3-4 times. They sat here for a few years then one day I was working up loads for a HK USP 45T, so I loaded those up and they finally went off without a problem even though the primers were already severely dented.