With professional perk, the 12.7 mm killed BOS paladins with a single head shot, but the 10mm wouldn't.
Use the 10mm for general purpose sneak and shoot - lost of parts and ammo, and it counts for concealed carry.
12.7 mm counts as the big gun.
Useful Sneaky weapons:
- 12.7 mm suppressed
- 10mm suppressed
- sniper rifle suppressed
- dynamite (reverse pickpocket...instakill)
- riot shotgun -- first shot w/slug will drop anything, next 11 in the mag prove deadly when his buddies come around the corner.
Happy hunting!