A loose primer pocket can cause flattening... when fired, the primer starts to back out of the pocket, then the case smashes back into it, flattening it around the edges. If the chamber is rough, it could retard the rearward movement of the case long enough to allow the primer to start backing out. This can happen with fairly mild loads, as well.... which makes the shooter think it's high pressure, when in fact, it's the opposite.
Made it to the range. Loaded up a handful of different combinations of bullets and powder. 100% better. Brass comes out clean and I was able to run the ammo that wouldn’t extract from the trip before. The groups look promising.
Thanks for all the input.