Cold, there was an article in one of the gun mags, maybe 2-3 years ago, about the bird shot (snake shot) rounds. Upshot was, pistols are much better than rifles, pattern-wise; 22 cals patterned better than larger calibers (maybe because they use #12 shot instead of #9); and pattern spread tends to be about 1 inch of spread per foot of range (kinda makes it a real short-range proposition, maybe 12-15 feet, and 8 is probably better!). Hope this helps!
Mark