I own a couple of Pedersoli repro screw barrel derringers. It can only be fed 10 grains of powder so it is unlikely to be dangerous. I load it with 10 grains of 777 under a .454 ball. This load can send that ball out at over 500 feet per second for a ME of 80ft/lbs energy. Not impressive by todays standards but I wouldn't want to stand in front of it. At close range it could be deadly.
Don