If you are using them in a break open single shot, a 10 gauge overshot card in the 12 gauge shells will suffice without any glue.
In a double barrel, you want some sort of glue so that the overshot wad will withstand the recoil of the first barrel.
What he said. I used Elmers glue with no problems when I first started reloading shot shells with bp. Now I use plastic shells cut off behind the crimp and roll crimped.