At a gun show a few years back I purchased a chamber reamer for .223 A few months later I came across a few hundred 5.56 whatever military blanks. Using bar stock, I turned a metal insert that matched a 10 ga shell and drilled a 15/64ths hole through it length wise. Then I used the chamber reamer to make a chamber in the base. The military blanks fire just great. I also made an insert to fire 410 blank shells that I load myself with 1f.