If you're using that RCBS press to prime, be sure it's mounted to a stiff strong table, that table has lots of weight, (or it's bolted to the floor), then put some muscle into priming those cases.
I can reiterate this. I just did 100 rounds of 45 Auto on my Ammo Plant. Had 5 cases not get primed because of the "bench" I'm using. I thought it would work out pretty well to put it on a wheeled table and just lock down the wheels. But the wiggle as the locked wheels rotate around, not even roll is enough to throw off the extra "oomph" on the downstroke to not seat a primer if you don't work twice as hard at it. I'm about ready to either dump the wheels and find a cart I can put on and off the bottom when I want to move it, or get rid of the wheeled idea entirely. For now, I'm going to start priming by hand.