i use a 10x32 2 inch taper head machine screw and nut.
I use JB weld or marine fix fast epoxy putty.
apply light grease to the screw threads only
thread on the nut just at the end
insert nut end into the recess in the stock and tighten the screw till snug..... a small washer (to be removed after) can be fited to the screw at the taper end to help it stay straight when tightened during this process.
once tightened, ram premixed JB weld or epoxy putty into the area around the nut end until covered. place a small strip of saran wrap or any plastic sheeting over the work area and press it all smooth. this will peel right off once cured, leaving a finished modification with no sanding or shaping to clean up.
then remove the screw once it has all hardened. the grease will act as a mold release and the screw should back out easily with a screw driver.
voila, a permanent repair
now, for those putting a chinese buttplate onto a g.i. stock..... you may have troubles opening the trap door as the mechanism on the chinese buttplate sticks out further than a g.i. buttplate. Under the hinge and lock of the trap door, I generally remove stock material with a dremel to clearance the hinge and lock so they can be utilized,