Edit, for Jack's point made:
OK, then change that last sentence to read " At 21 yards there is simply not much room for error."
Yes, there is a difference in pattern sizes at that range w/ full vs. open or skeet type chokes and most of us have observed ugly one sided breaks or even delayed breaks where the target was hit by an errant pellet [the proverbial golden BB] and only fractured and the centrifugal force finally caused the target to separate making for a break. The former breaks involve the 'not much' and the latter 'luck'.
Also, some loads patterned thru skeet bbls at 21 yds are smaller than we imagine, or at least that has been my observation on several ocassions.
