You could try the oversize #6 screws that Brownell's sells.
Link They sell the taps separately but jeez they're expensive.
I've no experience with these screws, maybe someone who does will jump in.
I have a screw like that in the thin part of a Mauser receiver, tightens down but feels like it could go further, doesn't come to a hard stop when it sould. Blue Loc-Tite has its uses. De-grease the threads to get the full strength. Not the ideal solution but it's worked for me.
