I think the genius of the Giss Dianas was that their recoilless design was potentially very expensive but they kept the costs down by making a huge quantity of them - in the case of the pistols by having both a fairly cheap budget model (mod 6) and a top-end match model (mod 10) - all with interchangeable parts. Which makes it all the more surprising that Diana dropped the ball so badly when it came to launching the model 75 Giss rifle.