I have used my 20 off and on for ringnecks for many years.. I usually use a ounce of #5's or 6's.. 5's are my first choice..
I also always have one of my 12's with 3 1/4 - 1 1/4 - #5'S. I for one do see a difference in killing birds with the heavier loads, although they are NOT always needed some days they are good to have..
If you have a #" 20 you can get the same load, and if it patterns well you are in tall clover..
Most of my pheasant guns have either a mod. or imp. mod. choke.. Mostly mod..
