I saw a wall musket-sized gun at the Germanisches Nationalmuseum in Nuremberg that used a metal block as a magazine. Individual chambers had been bored out of it to hold a charge of powder and ball, and since the whjole thing faced forward and stuck out sideways to the right, the worst possible effect of a misfire would bne more lead flying in the (very general) direction of the enemy (unlike, say, early revolver rifles, which would take the shooter's left hand off). Technically, this was clearly something people tried to get to work early, but I assume there must have been reasons (more economical than technological, probably) why they couldn't. At least the model at Nuremberg never made it into mass production.