Again, more good information . Thanks. As JFE mentions, the magazine feeding will be an issue to deal with. There are many posts that talk about the .375 feeding from a LE magazine with no problems, but unless the original Lee Speeds had a special mag for the .375, some magazine modification will be necessary and I am not sure at this point how successful they will be. As an experiment, since I have no 375-303 rounds to play with, I seated some 255gr Lymans very shallowly in some 38-55 cases (close, but not the same as the 375) and it is obvious that there will be issues with a straight-sided case. It looks as though modifications might be possible but it will require further tinkering to find out. I've looked for posts about modifying LE mags for this purpose, but no success yet. Cheers.