memtb,
The "problem" with larger 8-40 screws is their larger threads than on 6-48 screws. The larger threads result in the "unthreaded" portion of the body of the screw (which is what might shear) being just about exactly the same diameter as on finer-threaded 6-48s. But if they make you feel more confident....
Which is one reason I have sometimes epoxied bases to the actions of harder-recoiling rifles, which provides far more help in keeping the bases in place than either 6-48 or 8-40 screws. But eventually I tended to prefer actions with integral scope-mount bases, such as the CZ 550 and Rugers.
