I would just bore another hole in the forearm. Run down to the local hardware store and purchase the proper size booring bits so that the bottom of the holes will be flat. This will allow you to move the little washer from the old hole to the new one and have a nice solid base for the screw to pull down against. Then install a sling swivel stud in the old hole, or plug it with a bit of hardwood dowel.
I like the way the "full length" forearm looks on a pistol barrel too!