Out of interest, how were these 'rifles' regarded in Australiaand the USA
. Were they classed as totally inert and therefore not subject to any firearm rules or were they still regarded as firearms. When we were apprentices we'd often have these things to section as group projects. You had to have a real in-depth knowledge of the subject because you could be happilty drilling or milling something, only to discover that the viewing slot allowed a spring or part to drop out or jamb up!
As a little aside, regarding the Lithgow skeleton. If it was me (oh, hindsight is a wonderful thing of course...) I'd have SIDE sectioned the top of the cover instead of TOP sectioned as shown. That way, there would be a partially sectioned side and the other side would be totally complete