I am having the same issue on a dillon 750XL using hornady and now Mighty Armory sizing dies Speer and federal (and the odd browning) brass all don’t size properly and bullets fall down in the case even before expanding. These are brand new dies not old worn ones and the MA dies are supposed to be the latest and greatest thing. It’s frustrating because I have thousands of sorted and cleaned Speer and fc brass and nickel plated brass. As one of the guys stated earlier, they load fine on my single stage but I’ve got a Dillon 650xl and a 750xl for the sole purpose that I don’t have to use a single stage for pistol ammo. I measured the Id of my dies and they are well inside of spec. I’m going to try an undersized die as a last resort I guess.
Edit:
I have also measured my bullets I use a lot of Sierra and Everglades for bulk stuff and they are all good to go.
