Yes, you can shoot 375H&H in a .375Wby rifle but not in a .378. That is the best way to make .375Wby cases. There are no magazine problems with either the 300 nor the 375. They are just "improved" cartridges based on the H&H rounds. I consider the 300Wby and 375Wby the best ideas Mr. Weatherby ever had but I still prefer the H&H cartridges in their original form.