Children's modeling clay (sold in toy stores) works good for most recess' and dams - but paste wax is better for packing threaded areas.
I also paste wax that I use on the outside of the stock ( no sticky fingers or epoxy fingerprints) for the action screw or the stocking screw threads, so no epoxy sticks to either them, or their threaded hole.
The act of turning in the screw will push out a little bit of wax, but it doesn't usually effect the glass bedding, and is easily cleaned up afterward.
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