What makes a "Gunsmith" screwdriver is that it's NOT tapered in any direction like ordinary drivers.
Standard drivers are wedge shaped when viewed from front or side.
When these drivers are used on gun screws, the flat wedge shape tends to climb UP out of the slot, scarring the screw, and since it is a wedge shape, it only grips the screw by the upper edges of the slot.
This causes the edges of the slot to burr out.
From the front, the driver is also a tapered wedge shape.
When the driver is inserted in a deeper screw hole, the upper area of the drive scars up the outer edges of the hole.
A true gunsmith's driver has a hollow ground face. Due to the hollow grind, the lower part of the bit is parallel.
This bit grips the sides of the slot, not the top edge and applies all the torque to the stronger sides of the screw slot.
Since the driver is parallel, it doesn't cam up out of the slot.
The front of the driver is also parallel, so no matter how deep the hole is, the driver won't contact the edges of the hole and scar it up.