For jacks I use 1 1/4 oz of #5s from a 12 ga. I never change my light modified choke for anything. More choke might result in more kills when they are sitting at long distance, but a disadvantage on the close range runners.
I take tons of jacks while after cottontail, chukar, and quail. When not going after them specifically, I use 1 oz of #6 in my 20 ga with a LM choke. This load will still drop jacks without a problem, but #5s from the 12ga drops them with noticeably more authority when they get out a little further or the hit is marginal. Overall, I prefer rifles if only after jacks just for the Challenge and practice.
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