Normal screwdrivers for slotted screws are tapered, which makes it easy to slot them in quickly but means that they only contact the slot at the top corners.
A gunsmiths screwdriver is hollow ground with a parallel tip that engages fully with the slot in the screw.
Slower, a little, but much less likely to marr the screw head. Hardened, polished and lacquered blades, stained beech handle with knurled brass ferrule.
Set of 3 - 3/16, 1/4 and 5/16 inch