I'm trying to finish a fiberglass stock blank and I'm having trouble getting the action to drop all the way in. The factory said the blank was "nominally inletted" and so far I've had to do a lot of grinding & sanding. The barreled action now drops almost all the way in, but seems to stop about 1/16" from flush at the tang, and I can't find whats stopping it.
How can I find out where the problem is ?

Anaconda, go down to a auto supply store and get some Permatex Prussian blue. It is like a blue oil paint. Use a small brush or a cotton Q tip and brush it on the action. Then put it back in the stock and when you take it out you will see where the action is touching. Remove the spots of blue and soon it will drop in where you want it.

Or do the same thing that Chic suggests, using lipstick.

Cold bore,
Are you trying to get him in trouble.
his wife or girl friend might start asking questions with lip stick laying around the work bench , he might get it on his collar by accident.