Hope this doesn'r sound too extraneous.... Does anyone know if the 7.62x54R Bren (etc) barrel conversions from .303 Enfield can still safely fire original .303 rounds once rechambered ??? I believe that both those rimmed rounds headspace off the rims.
Perhaps a test fixture/rifle (P-14 rechambered from .303 to 7.62x54R) would be worth trying. This might be a true "multi-cultural" chambering.
VD