I think you're chasing a "willow-the-whist". A 300 yard .375 cartridge just requires a longer round than any levergun can handle, the .375 H&H is barely a 300 yard round. You will need a 270 grain spirepoint at 27-2800 fps.

I've had a couple of Rossi .357s and one Marlin .357 and they just don't compare, the Marlin is built to be a real rifle and the accuracy is 1 1/2 moa easily. The Rossis are built cheap to sell cheap but they don't sell cheap these days and accuracy is minute of paper plate. Now those Rossis were qu...