The issue with these rifles is the chamber specs, some chambers are too tight to accept a round with a .379" bullet, even though the bore may be .379-.380". I used Lyman dies with mine and the Lyman "M" die will open the case neck to allow seating of .379" bullets and perhaps even larger although .379" is the largest I ever tried. My chamber accepted .379" bullets with no problem but I doubt it would take .380" and others have had problems with .379s.