12 vs. 20
Reading is fundamental. Remember RIF?
Take a moment to look at the velocity and the payload of your shotshells. The velocity will be very similar across the various gauges, typically between 1000-1500 FPS. What can differ is the weight of the shot or the weight of the slug.
Even then there are 20 gauge loads that will equal a 12 gauge. Esp. if you include 3" 20 gauge.
Recoil is about the weight of the shot charge, and the weight of the shotgun. The velocity is Approx. the same. Yes the velocity CAN differ, and that is true of all the different gauges.
Also remember as the gauge goes down, the weight of the shotgun usually goes down with it.
My point is don't buy in to 20 gauge for recoil reduction, a 20 can kick harder than a 12.
I keep it simple, a heavy gun, and no more velocity than what I need to break clay's with authority. For me that's an ounce of 8's at about 1150.
Oh and that other ingredient........a gun that fits the shooter. In fact this is the most important. Both for comfort, and your score.
I remember my little brother borrowing my very lightweight 3" 20 ga. Kicked the snot out of him. He was thinking, it's a 20 gauge and they don't kick hard.