Pretty sure a real gunsmith could fit the 300 barrel to the 250 frame. the headspace would have to be checked with go-no-go gauges and the chamber might have to be cut deeper. the 250 rotor would have to have the neck area reworked to fit the 300 bullet. A 250 case would work in a 300 rotor but not reverse.I have only worked with the rimmed cases as its pretty easy. Don