I have an older S&K '03 mount. The way it mounts is that it has a ring to go around the barrel shank, at the front. Then it has a set up that kind of hooks and clamps at the rear receiver bridge. I imagine that the '03A3 mount slides onto the reverse dovetail and then is secured by a set screw. Does your rifle have a dove tail slot cut into the rear receiver bridge? Or does it have the raised dovetail (often called pins in furniture construction)?