If you grind away the insert rim where it would contact the extractor of the gun itself, the extractor on a ten gauge gun will extract a 12 gauge shell and the insert should remain in the gun. That's the way I use mine although other methods are just as convenient. I am using hand made inserts, but the gauge mates should work the same way if modified. I have bought a full set of ten gauge gauge mates but have not yet used them. I have used the hand made inserts in eight and ten gauge for years with good success. I have ground various amounts of the rim away to facilitate removal of empties. It has always been an experimental process.