I have often used GaugeMates in 10 gauge shotguns in order to shoot 12 gauge ammo at clay birds. I always used either Remington STS or Winchester AA ammo, since that is recommended by GaugeMate in order to avoid sticking. The GaugeMates worked like a charm for me. I would recommend them, if they are still made or if you can pick up a set on Ebay. I do not have any experience with the situation Stan mentions, but my "10 into 12 gauge" purposes, the GaugeMate Golds were excellent.

Rich