I've been wondering about something, having recently bought a nice gun cleaning accessory kit that contains a set of three unground screwdrivers (turnscrews in Brit speak). If turnscrew is the proper British name for what we call a screwdriver, why is what we call a screw called a pin in British gun speak? Why wouldn't the Brits call the tool a turn pin? Why do you gents use a turnscrew to turn a pin?

Maybe there's some English doublegun history that would help explain that apparent contradiction ?