This would take a little extra confidence in your tinkering ability, but you could put the lugged barrel in a vise, clamping only the lug and make a small cut just under the latch shelf on the back of the underlug that faces the breech face, making it deep enough to insert a thin flat blade screwdriver blade, and use light taps to evenly spread the gap to raise the latch shelf.
It would take some tedious fitting and working extra slow, but it would be better than an epoxy shim in my opinion.
You could then fill the cut or gap with JB weld, and touch up with a small file or stone, and be good to go.