Ha, I read an interesting Theory someone put up on the net concerning the origins of "son of a gun" ,they propose that it came back from the British Navy where the ships would pull into
port and several sporting ladies would service the crew and being such tight quarters understanding its standing in line room only, the ladies would assume the position over a cannons barrel and as is the nature of such proclivities, children were brought forth, the sporting ladies being totally clueless as to who the father was would log " son of a gun" when seeking the rights of the child to being a Sovereign subject to the crown,,,, 
good as any,,,I reckon