I've recent started reloading pistol ammo where all of my other reloading has been for bolt action rifles. I'm reloading 45acp and shooting it out of a m&p45, the issue is I've been cycling some rounds thru the gun manually and not firing just to see how there feeding and I've had a few that the after being cycled once the bullet is getting pushed down in the casing a little almost causing a compressed load. Ive bought some brass new some once fired and some has been given to me by folks at the range. I'm loading them with 5gr of unique with a 200gr fmj speer bullet. Ive checked each cartridge for proper length and wigth and checked every round for OAL and its all good. I also used a full length resizing die on all the rounds. Any info as to why its doing this?