pinning scope rail

having trouble with scope rail staying put on my 50 bmg rifle, the 5 screws won't hold it for long. i want to make it solid, i can tig it in place or i can pin it. pinning will be tried first, what is the needed thous. between drill size and pin dia. for a drive in fit(will freeze the pins for a tighter fit if there is a need) work will be done on a bridgeport mill.

thanks kurt

For an interference fit, make the hole 2 thousandths (0.002") in diameter LESS than size of pin, then press-fit the pin. DO NOT freeze the pins; they will be very brittle and will break/shatter if struck.