.375 is a bit small for most 38-55 s they use a .377 bullet (jacketed) your bore is one of the oversized That has kept me a way. With a 380 groove. I would try to use a .381, .382 diameter bullet(cast), but like you say it won't chamber in a lot of them, plus finding a bullet that diameter . I would be inclined to use a softer cast bullet hoping it would bump up a bit. All these thoughts are what kept me from getting one. Now that it sounds like things might be squared around though, who knows.