I agree completely with Goodnews.
The "secret" to killing pheasants at normal ranges is hard #6 shot (or thereabouts) that patterns well. A lot of 20-gauges won't pattern #5 or #4 shot well, and for that matter a lot of 12's won't either, especially if full choke. I have killed a pile of pheasants cleanly with 28- and 20-gauge shotguns using 7/8 and 1 ounce of good, hard #6 shot out to 40 yards. In fact I have gotten about the same results with #7 shot (NOT 7-1/2) in both gauges.
If you aren't killing pheasants cleanly to 40 yards with a load like that then either your shotgun doesn't fit or you are simply fringing the birds. And believe me, I have patterned enough shotguns to know that a thin fringe happens with all gauges, not just the smaller ones.
Only past 40 yards does a 12-gauge make much difference, but even then you have to pattern the gun to find what loads it really likes, and are generally better off with 1-1/4 or maybe 1-3/8 ounce of good hard #5 shot than anything heavier. Good pattern density kills more birds cleanly than fewer, bigger shot, if the shot you use penetrates deeply enough. Another good size is 5-1/2, if you handload.
