I like the .375 Winchester but I have found it to be crimp sensitive. You can work with roll crimp and the Lee factory crimp die and improve accuracy a bit but it is hard to keep groups under 2" on an everyday basis.
My best accuracy results were with the 200 grain Sierra bullet driven as fast as I could get it to go.
The .375 Winchester is powder capacity limited and it is difficult to compare it to the .307 and .356 cartridges.
Back in the Marlin Talk board days there were some people who were getting a bit better accuracy than I can muster. The trick seemed to be using as largea diameter cast bullet as would chamber. The throats being a bit large and the origin of the rifling a bit abrupt.
My preferred powder has always been Hodgdon 4198. Alliant Reloder 7 works fine but I am able to generate slightly higher velocities and perhaps just a bit better accuracy using H4198.For our little West Texas deer the Sierra 200 grain bullet at 2,300 fps+ is the best load. The Sierra bullet is tough and penetrates well. I find the 220 grain Hornady does not open up quickly enough on our light framed deer.
Hodgdon Benchmark will deliver 2,294 fps with accuracy in the 2"circle on most days. Bench mark is very easy to work with, you just cannot get enough into the case.
Alliant Reloder 10x comes up a little short velocity wise - 2,280 fps is about the top end with the 200 grain bullet - but it will deliver accuracy from the starting load to the top load. It seems very predictable.
Hodgdon 322 comes up a bit short in velocity - 2,270 fps is about tops with the 200 grain bullet. H322 has the bad habit of leaving a few hard little kernals in the chamber when you extract the case and dimpling the next case fired.
My critters don't hunt me so the heavy bullets are not in general use for me. The 255 grain bullets run at cast bullet velocities so I shoot the 250 grain Lee bullet as my primary lead bullet. Cast sift or heat treated they do about as well as any I have tried.
