I bought a 4x8 sheet of 3/8" steel plate for gongs and such, some years ago. I still have half a sheet, it was pricey but it goes a long way.
For heavier calibers, get thicker plate. - I use my 3/8ths-inch stuff for rimfires and handguns.
Edited by charlesb (02/04/16 12:10 PM)
Kind regards, charlesb