For HD? I know 00 seems to be the very popular from what I have read for HD but it seems like 0 Buck has a better pellet count to weight ratio at 12 .32 cal pellets for a standard 2 3/4 shell vs 8 or 9 .33 cal pellets in a standard shell. Just wondering why it's not used or talked about much. I guess you can make the same argument for 1 buck but I have not tried it yet, I wouldn't want to go below .30 cal pellets because I feel that they lack penetration for the intended purpose IMHO.