I had at home one of those tubular apple corers with the wooden push rod to push out the core. Just for the heck of it I used it to punch out a couple of felt wads and they were almost a perfect 12 gauge. They were just a bit too big, so I changed the shape of the cutting end so the bevel was cutting on the inside of the tube and that helped. I know it is a weird coincidence. I have made wad cutters for other people up to 8 gauge !! They are easy to make, all you need is one of the plastic chairs someone is throwing away with the tubular leg that is skinny at the bottom and wide at the top. Somewhere as the tube gets wider and wider is your 12 gauge diameter. You have to keep cutting and filing, but it works. You need an inner/outer vernier caliper so you can measure the inside of the tube as you go along. When you get to .730, stop. go up about 6 inches, cut it off there and file and hone the outer diameter end until it's razor sharp. Heat it and quench it in oil to harden the edge and you have a wad cutter in 12 gauge. There are 4 wad cutters on every table or chair with graduating tubular legs. I use a rubber dead blow hammer on the pounding end. It doesn't damage your homemade tube cutter, it doesn't hurt the hammer and the dead blow hammer helps drive the cutting edge thru wad material or cardboard for over powder and shot cards.
Ohio Rusty