I believe that regulation within 3" at 50 yds is considered good for a double. Think about the game you want to shoot and the normal range and size of the vital area. Same principal as setting up the "point blank" on a bolt gun. (ie "Point Blank" in the correct sense, meaning the maximum distance that you can point of aim and guarantee a hit in the the "kill zone" eg I recently set up my 375H&H bolt gun for pigs with a point blank of 200yds. The assumed "kill zone" is a 6" circle - my rifle shoots 1 1/2" high at 100yds and 2" low at 200yds and it shoots MOA at both ranges, so 200yrds is the limit in my case.)