If you've got a safe place to try, check this combination out: glue one of those small exploding targets to a can of spray paint. Be sure you are 100 yards away. If you can hit the exploding target dead on and go through the can of paint, you'll get a 10 foot fireball.

A more environmentally friendly explosion is a hit on a block of ice. When the temp gets below freezing I fill 2 liter Pepsi bottles and put them outside overnight. When I hit them with a .308 I get a good spray, and I can usually get 2 or 3 hits on each bottle.