I use the same system for trigger plates, barrel slide escutcheons, and tenons. I drill a series of holes centre punched along a line, each hole touching the last if I can manage it. Then a jeweller's saw to remove the webs of metal between the holes, then needle files to clean up the slot. Barrel slides are often less than 1/16" thick, so the slots are correspondingly thin, but my trigger shoe is normally between 1/16" and 3/32" thick, so the slot is wider there and easier to cut.