.375 Win is essentially a very much higher pressure version of the .38-55. The case is a fraction shorter, just the opposite of the relationship between most "special" and "magnum" revolver cartridges. The only reason I can think of is that perhaps it'd feed a little better with the existing bullets in the Winchester 94. That's a guess, though. I've made .375 Win cases from .38-55 but I do not load maximum loads in them.
.375 Win brass is hard to find. Hornady's 220 grain flat point behaves very well. It is hard to get a max load of RL7 in the case even with a drop tube but it shoots pretty well, around 1.5 MOA with iron sights in the '94 Big Bore I had.
