If the bullets look good...all the gooves well filled out, no big wrinkles, and the base filled out well (the edges not rounded off or ineven) then you cast them right reguardless of the weight.
Loading is pretty much idential to the manual instructions for loading straight walled pistol cases...same idea, need a three die set.
Had a .375W and a 38/55...ended up keeping the 38/55. I would load to two levels: full power and low power plinking. For full power for me was 32gr. of 3031...some loading manuals will go a good bit higher, but past this point (about 1555fps) the 375 would make improved cylinder patterns. Oddly the 38/55 would toss the same bullet accuratly at about 150fps more velocity...cold be a gun to gun variation, or it could be the slower rifling twist of the 38/55.
The light "plinking" load was the same for either the 38/55 or the 375W. Taken from the RCBS Cast Bullet manual (#1), I use 7gr. of red Dot for all of 1025fps. I still use theat load for most of my off-hand practice, rolling tin cans for fun, and general fun.
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if you want to use jacketed bullets, will direct you to the "Hawk" line (they are on line)...about perfect bullets for the velocity.