NOT TRYING TO BREAK ANY LAWS HERE, BUT HERE'S THE QUESTION.....?

So I went on a little hunting, well, "plinking" trip to Pennsylvania, and I was able to buy some black powder, which we can't get in the state that I live in. I've got the cannon fuse, and I'm gonna buy a hot glue gun from wal-mart, but without having to dangerously mix magnesium oxide in with the powder, how can I get the biggest bang using the smallest amount of powder..... Alll speculation welcome. Thx. - john (a pseudonym, of course) (and no, no metal can be recommended, we can't risk injuries doing this because there will be children within a hundred yards)