Hey Bob,
No scope stop with mine either.
My breech is not chromed either, like Dave said it's like a matte nickel finish.
Dave is correct, the screw acts as the stop for the riser.
As for the riser itself,,,, my .177 CFX also has the same riser setup and I can tell you that it's been rock solid on the receiver since day 1 with no movement whatsoever. I check it periodically but every time I check the screws are always rock solid tight.
Best of luck with the gun.. Mine is sittin down in my gun vise. I installed a Golden Antler scope w/Accushot 2 piece medium mounts last night so I'm gonna let the loc-tite cure for 24 hours before I sight her in. By the way,,, the rings that came with the scope/rifle actually look decent, but I had a couple pair of the Accushot rings lying on my supply shelf so I went with them.
Jeff