I've just put one the new Oz seals on my Brocock Indy (Basically a Gamo action), it's the seal that covers the whole dovetail and reduces the lost volume, seem to fit pretty well but the normal type seal they do does seem a bot loose, I didn't size that one as I think I'll just shoot that one in, it'll be interesting to see what the Maccari seal is like as I've never had one of those before.
Pete