Trench art got it's name from WW1 when the soldiers in the trenches had lots of free time on their hands and would make vases, ash trays etc. out of the the empty howitzer shells. Usually it's large caliber cannon shells but goes down to small arms size too.

The more elaborate, the more it's worth. Search trench art on ebay to see more of it.

BTW, I picked up 520 lbs. of scrap steel Friday afternoon at one of the sites I check. People like to shoot up propane tanks and stuff like that. Not alot of scrap but it netted me $57.50 for about 10 minutes of work.