Holy crap!!! That looks like all sorts of fun.
I have only heard of these refered to as 3.5 inch RLs and freely admit my knowledge on them is pretty much limited to that alone. Looks cool, nice piece.
If I recall correctly they are electrically fired. The pistol grip trigger is a generator when u squeeze it , it sends an electrical charge to the copper band around the base of the ammo
Yep I fired them back around 1977 -78. We just called it the 3.5. We were using up the last of the ammo that the base had.