Brass drivers are useless for gun work.
The idea is that brass won't damage the slots, but the truth is, the soft brass deforms, slips out, and damages the slots.
A properly made, high quality gun screwdriver won't damage the screw since it fits the slot properly and puts all the pressure on the sides of the slot.
A good gun screwdriver should be so hard that if you over stress the screw the driver will break.
This is by intent. It's much cheaper, faster, and easier to replace a screwdriver bit than an expensive, and possibly unobtainable gun screw.