but you wouldnt need a piston if it was blowback.
i think thats the terminology where i misinterpreted your post.
that would be cool with a rimfire. with the x25 or 9mm though, i thnk taking that much weight off of th ecarrier would kill the design for blowback. BUT that might make a gas op one more of a possibility too, with less carrier mass for the lower amt of gas to move ??