They include the spent casing because some state laws require a round for 'ballistic-fingerprinting', which is a different process from the 'test firing' as I understand it. I don't happen to know how many guns are 'proof' fired, but I think all are test fired for function which would probably be an entire cylinder or magazine, depending on the type of weapon. I know that some SS Rugers I've gotten new have come with faint blast marks on all 6 cylinder chambers, but I've never purchased a new blued gun that showed any sign of blast rings.