The other guys answered your question, but where you state your primers are looking a little flattened,
if you are not loading to closer to max pressure, that can also cause the primers to flatten.
I do a lot of downloads for kids use, working with BSA and also new female shooters.
I am currently developing some light loads for a campfire member's grand kids use... with Win 452 AA shot gun powder.
The load is 8.5 grains in a 223 case. It isn't very high pressure, but the primers come out flattened... yet when resizing the cases, they don't offer much resistance with the loading die, doing a F/L resize.
by the way, I support FC363s response the most.
Instead of just trying to barely size the case, I play with bullet seating depth instead to barely touch the lands. That is my preferred method.
