I shoot 20 grains of 4227 in my ruger SBH and Marlin 1894 under a 325 grain cast bullet.
If you could share what powders you have and some info on the bullet we could help you more.
Question.... Why would you powder coat and lube ?
Especially a hard bullet made from wheel weights.
Ok.. Why do you think you have to use all those redundancys to achieve your goal. I can see the gas check and the correct lube, but why the extra work of powder coating ?
I assume you understand the more you fool with / change a bullet. The more variables you add for decreased performance.
I have pushed 30 cal bullets to 18 to 1900 fps without any undue leading..
... I can say from experience that at 50 yards this bullet will go in and out of a deer lengthwise.