Nosler and R-P brass, 243. 3rd loading on the Nosler, 2nd loading on the R-P. Primers wouldn't go into the pockets. Primers are WLR.
Tried two other 100 packs before I found some that would go in. Some of the cases felt like I was forcing the primer past a crimp.

What gives? Primers over-sized slightly?

Measure them with your calipers...both the primers and the primer pockets. See what's going on.

Hornady makes a couple tools that you need. A primer pocket crimp remover, and a primer pocket bottom reamer. The first tool removes the crimp and trues up the sides of the pocket, the second tool flattens out the bottom and corrects the depth if shallow. The names of the tools are wrong, but you get the idea.

I think what Cast was looking for is a primer pocket reamer which will help true up the bottom of the pocket, and a primer pocket swager which trues up the sides and will swage out the crimp. Unfortunately I don't think either of those will do anything for this. None of those cases should have a crimp, plus you said they had already been reloaded. It's a headscratcher for sure. What dies are you using? I know small base dies size cases at the bottom, but I've never heard of this issue. Have you tried any other primers? Did you clean the pockets? Do you seat them with hand tool or with a press? Anyway, just some things to check.

What are you using to prime the cases with? If it's a hand primer, then you will feel it a lot more than on a press mounted primer.

I've never seen pockets get tighter. But you can get debris in there causing it to feel tighter.

Hand-primer is what I'm using. This is after I have used the Hornady tool to clean out the primer pockets. No visible crimp on them and the 2nd box of the 1000 I opened loaded in just fine.
I'll break out the calipers tonight and see if there's any difference.

Sounds like some slightly out of spec primers. You might find someone who would want them...some guys keep their necks annealed and are very careful about resizing to the extent that they quit using brass only because the primer pockets start getting too loose.

Measured about 25 that 'didn't fit' last night. Measurement was .001-.005 larger than the others that did fit. Found my answer.