Welcome to our forum, Stimey!! That screw should be .0015" off the barrel, it's just there to support larger scopes when mounted on the end of the rail, this spec comes direct from H&R CS, it's also listed in the FAQ and Help sticky which you should read, lots of info in there for us Handiholics!! I prefer the standard rail for most scopes, I think I've only used the end slot on one barrel out of 29 barrels.

Tim