I was looking to make my own Overshot cards and I tried to look it up and what I read was that a 5/8 punch should be the size I'm looking for.

So bought a 5/8 punch and punched some cardboard that I had saved up. When I placed it in the empty hull it looked way to small. I have never rolled my own shotgun shells this is my first time. Will it look different after I roll crimp it will it fit? Or do I have the wrong size punch?

Or it could also be that I have not gotten the punch sharp enough yet also bought it used but new. ( Wish they would have said so dull it can't cut through paper.) Thanks!

You are way undersized - 12ga is .72ish inches in diameter, 5/8 is closer to .40

Quick google shows commercial ones being sold are .720 ... so like 23/32nd

So be closer to getting a 18mm punch. It's just a little off. Thanks!

When I was messing with it I got an 18mm leather punch for doing 12 gauge.
One similar to this one.



I also found this chart here:

8 gauge, 0.835 dia, 27/32nds, 21.2 mm arch punch

10 gauge, 0.775 dia, 49/64ths, 19.50 mm

12 gauge, 0.729 dia, 23/32nds, 18.25 mm

14 gauge, 0.693 dia, 11/16ths, 17.50 mm

16 gauge, 0.663 dia, 21/32nds, 16.75 mm

18 gauge, 0.637 dia, 41/64ths, 16.25 mm

20 gauge, 0.615 dia, 39/64ths, 15.50 mm

24 gauge, 0.579 dia, 37/64ths, 14.50 mm

28 gauge, 0.550 dia, 35/64ths, 14.00 mm

.410 bore, .410 dia, 13/32nds, 10.25 mm