Freind of mine had a chunk of property and a dozer. Dugout a huge rectangular pit. Laid in reinforced concrete on the bottom and the sides. Then bought a bunch of those shipping containers and laid four end to end (no doors). He had four rows of theis which were perpedicular to a couple of containers that we placed side by side. Then took Ibeams and covered the top spaning the structure side to side. Then poured concrete ontop then back filled and coverd with the excavated dirt. The rest he used as berms on his property.

I havn't done it justice with the discription I have given but, it was pretty cool. Had and acces from his basement and a fan system for the lead. Backdrop to collect the rounds and a storage place for his ammo, guns and a place to work on the guns. Last I heard he was since added onto it though I don't know what he did.