Great gun and guage! Good for you! 20's will kill "almost" as well as 12's...the obvious differences are less payload and slower velocities. In trap shooting at the range, screw in a full choke and shoot #8's and you'll do as well as a 12ga at 16yds (I used to shoot 7/8 an 1oz loads thru my 12ga for practice). I've killed em all with a 20ga, and to think of it with my 28ga that I had also. Like most sports, it's all about placement.
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..."the clock looked at me just like the devil in disguise"...