(jumpin' in a bit late - surfin' for some slug info ... )
Perhaps even an initial load of #4 buck for the rabbits - less shot to pick out & (no idea what a 2-3/4 load would do) but a Fed Premium 3" #4 buck mag will do 41 .22/.23 cal pellets! - not too terribly shabby. I'd figure an ~1/5-1/4 reduction at 2-3/4 ... & ought to do a rabbit at your stated 10-15 yards, or so.
& really couldn't hurt one bit for a serious "frangible" at 10 yards, for a bear-size critter. Just a thought. Better pattern to be sure.
May be that ~30 (or so) #4 bucks, w/a 50% pattern on a r'bit at 15 yards may be a bit much .... do let us know
