Either the .374449 Lyman or the RBCS .375, 250gr. bullet will work fine. The RCBS bullet has been a good shooting bullet for me, in 3, .375's. The #375449 also shot well in my BRNO .375H&H back in the 70's. I ran the RCBS bullet to 2,800fps (hardened & W/LBT Blue) in a .375H&H and still held onto 1 1/2" at 100 meters.

For a jacketed all-round bullet in that small capacity case, I'd go with the 225gr. Hornady. Deer, mose, elk bear- whatever. You should be able to hit 2,350fps to 2,450fps with it.