I've had to do this several times. It helps if you have an idea of where you suspect that it's making contact. I use a tube of red lipstick that I sourced from my wife's war paint cabinet. Put it on the part of the trigger that you think is the offending part. Doesn't take much, so don't glob it on there. Then very carefully lower the action into the stock and press down slightly. Remove it carefully and look into the stock for a red mark. Dremel out the red part, plus a hair for clearance. Lather, rinse, repeat, until proper function is achieved.