Your choice of a buckshot load should be made based on which patterns the best, pattern density being more important than pattern size. The inch pattern spread to yard of range is a generality, but is close enough for government work. But lets take a look at the actual patterns produced by Federal Premium 3" 00 Buck (which I've had a tough time finding) from my open choke 12 ga 590 as an example. At 5 yards there were two holes in the cardboard, an elongated hole from the wad, and a round 1.5" hole from the shot column, not bad when the generality suggests a 5" pattern for a shot from 5 yards. The 10 yard pattern measured 2.75" wide by 2" high, and this was due to one pellet hitting high and one pellet hitting left out of the otherwise tight cluster, 10 of the 12 pellets produced a 1.25" wide by 1" high pattern. The one consistent element of the shotgun is it's inconsistency, and the 15 and 20 yard patterns prove the point. At 15 yards the pattern opened up to 7.25" high by 8.75" wide, where the 20 yard pattern measured 4.5" high by 6" wide. Who would have seen that coming? And no, I did not mix up the 15 and 20 yard patterns. I expect this would not occur again if I repeated the test, but then again it might, or there might be some other anomaly. The final pattern was at 25 yards, which I consider the maximum effective range of buckshot, and it measured 11.5" high and 11.25 wide. I've patterned many different brands of buckshot, and in my gun the Federal Premium 00 Buck patterns the best, significantly better than the exceedingly expensive Hevi-Shot 00 Buck loads, which were the best until yesterday.
Every different shotgun barrel will pattern differently, regardless of choke. Every different manufacture of shell will pattern differently, and as this latest test indicates, anomalies will occur even within shells of the same make and load. That's just how it is. As a rule these variations and anomalies don't matter very much, as buckshot is not used for fine work, but if you have a gun-shell combination that produces tight patterns, there is little leeway for poor marksmanship, particularly at very short range, which has long been a stated advantage of using buckshot over a slug or rifle bullet. The real advantage is that a great deal of destructive force can be put on the target, without the over penetration of a slug or rifle bullet. You might well point out that the use of 00 buckshot will indeed result in a pass through of a live target, the difference is that each 50 gr .33 caliber pellet has little velocity left after say 18" of penetration of tissue, compared to a 400-600 gr slug, so the down range danger to people or property is dramatically reduced. This is the reason why some densely populated areas in the US require buckshot only during their deer hunting seasons.
