I just brought this one home. It has "crown, GR, crossed swords, P" faintly on top, "M601" on the hammer, serial on the barrel's left, and unreadable remnants of instruction stickers on top and left of the receiver, some warning about "this line". My take is it is a British Naval line thrower, don't know the calibre, but it is bigger than 12g. Does anyone know its name, what the warnings say, and what ammo/projectile it fired? Pics would be nice, or a website name.