Gauge/ Caliber Weight/gr.
Balls/lb.
8 .835 875
10 .776 700
12 .730 583
13 .710 538
14 .693 500
16 .663 438
20 .615 350
24 .579 292
28 .550 250
Since a 12 gauge is .730 inches.. what would happen if you took a 3/4 inch pipe ... say made of copper or brass, with a file sharpened the edges.. and then using a mallet, cut your wedges with that. They would be just about the right size and should be a nice snug fit.