RE: How much black powder in a 30/30 load?
You don't need much tin- the tin is for filling out the gooves in the mould, not for hardness. I typically cut an 18" piece of 50/50 solder wire and drop it into a pot of 10 lbs of cleaned up w/w metal to get desired results.
As for shooting BP in the 30/30, why? The 30/30 contrary to popular belief was never a BP cartridge, and you can expect your rifle to foul like crazy and have poor accuracy using BP.