Sure it's for real. It's an evaluation of their performance with respect to a specific special interest, the 2nd Amendment.
Would you be suprised if I told you other special interest groups rate politicians? For instance, CNET News.com ranks every member of the U.S. Congress based on their technology-related votes.
If you have a special interest, you can probably easily find a group with the same interest that will "sort" politicians for you.
The NRA does a fine job of sorting out those who would diminish the 2nd. Obama is one of those, Hillary is another.