I second the tannerite idea.....Last fall I was a a neighbors place doing some plinking with my new AR.  The railroad used to go through his place and there are still a few wood post pilings in the ground where a bridge was at.  We had four pounds of tannerite that was begging to be used so we set it at the base of one of the pilings.  They appeared to be about 16" in diameter and cut off about two feet above the ground.  It was in pretty poor shape and rotten already too so we could get the package wedged into it a little.  We paced off 100 yards....and then took a few more steps.  It made a BIG boom....and the piling disappeared.  When I got home (1/2 mile away) my wife said "what the he** was that!...The windows rattled on the house!".......Next time I'm trying six lbs!