Soft ? Not really. Not hardened tho. Proper fit of screwdriver for any gun screw is a must if one is to avoid marring screws and fitments.
Proper fit and good quality screwdrivers belong in dedicated gun gear stash. If it fits side plate screw, don't use it to pry lid off of paint can....etc.
Sorry you buggered the nut, at least replacements are available and not terribly pricey.
Sam......if it can be broken, I have.