What the...?
All they are doing is boring the case out a little more to fit a larger sleeve and piston. O.S. uses the same size case size in the cv.12 and cv.15, Ofna does the same with the force.12 and force.15 and even the saturn .17 they made for a while. I have discussed this a little bit with a guy who does custom engines for some top club racers in So Cal. I had a os cz .12 done by him 6 years ago and it was super fast, I dont know where he is anymore, when I met him he was a mechanic for team kawisaki's supercross racing team. He told me the only disadvatage of the larger piston and sleeve was a slight dropoff in durability. (fewer rebuilds do to case warping over time)