This is a neat series, very interesting too. There's a place in Russia that makes working micro weapons, full auto AK47s, some Civil War era weapons that are tiny and they work. The owner of the place explains some of the reverse engineering at 1/2 to 1/3 scale. He said you can just make the steel half as thick because it isn't strong enough. So the engineers had to work out an equation for the wall strength. I'll link to the shooting one. The other two Part 1 and Part 2 are interesting also but those videos are more about the process of manufacturing the guns.