Ive used 4%-5% TIN, and 95% WW alloy with a gas check bullet in my 375 H&H for decades
ww 748 powder works ok.
RL7, and IMR 3031 all work ok
https://www.midsouthshooterssupply.c...iber-264-grain

https://www.accuratemolds.com/bullet...bullet=38-220B

https://www.sagesoutdoors.com/375-38-55-caliber-gator-gas-checks/

http://garage.grumpysperformance.com/index.php?threads/bullet-lube.4835/#post-84993




get a
RCBS CAST BULLET MANUAL

Lyman Cast Bullet manual


I cast hot enough to look mildly frosted over the total surface and drop the hot bullets into a 5 gallon bucket of cold water
you want a MINIMUM BHN of 18 or harder 19-20 is about ideal for accuracy, at about 1800-1900 fps, 18-19 performs decently on hogs/deer with proper shot placement, if you don't get the accuracy you require with a gas check bullet sized and properly lubed at about .377 try a bit harder bhn, but thats rarely required, obviously powder burn rates and rifling twist rates, bore smoothness, effect the accuracy
http://www.lasc.us/Fryxell_Book_Chap...Metallurgy.htm