The way I've seen it done is by making a tiny flat washer out of the thinnest shim stock you have, then placing it under the head of the pin and tightening it down, then verifying the position of the slot. If more is needed you go to the next thicker shim stock. Simple trial and error.
Sorta like shimming the hook on a double gun that's not worth paying to have it put back on face. Like my BSS duck gun.
Dustin, I've read about adjusting the timing of a screw slot by doing exactly what Stan is saying, as an alternative to either machining a new screw or making adjustments to an existing screw by either adding or removing metal from the bottom of the screw head. The "shim" or washer can be made out of very thin sheet metal, plastic shim stock, or even waxed or oiled paper.
If you know the pitch of the screw threads, you can even calculate how thick the shim needs to be to move the slot the desired amount. In this case, the head needs to turn 90 degrees either way to align the slot at a 6:00-- 12:00 position. So if the thread pitch is 32 TPI, you would divide 1 by 32 which would equal .03125" for each full turn. Then divide that .03125 by 4 and the result would be .0078125" for a quarter turn. So a shim or washer .008" thick would get you very close to the 90 degrees of movement needed to align the slot.
Of course, there are various ways to get to the same result which have been mentioned. One other way would be to cut the countersink for the screw head a wee bit deeper. But it may just be a matter of a screw which is either turned in a quarter turn too tight or too loose. If it is already good and tight with a good hollow ground screwdriver, cranking even tighter with a brace or using more force also risks exceeding the yield strength of the screw, or even breaking it
