thats how we did it, with a drill press and dremel.
used the dremel to take that top part off, than put it in the drill press with an xy axis vise.
took time and drilled small holes in middle, than bigger and bigger, than went a little deeper and deeper.
with these same tools if I did another one I'm confident I could get it done pretty quickly.
now the question is, do I dare go with a 7/62x39 upper? its $00.20 a round cheaper.....
or the 223 and have a million options for types of ammo