Jrhunter25 wrote: The reason I am going with 4 is that the 20 has smaller shot size than the 12 gauge ( I think ) and the shot oz. is lighter.
I am not sure what you are saying here. The shot size does not differ between gauges.
The ounces of shot, while usually less in a 20 gauge, is determined by the type of shell. Such as magnum or a target load. You can find 1 1/4 ounce shot loads in both 20 and 12 gauges. The number of shot in a load is determined by the ounce of shot in the load and the size of the shot. In a 1 1/4 ounce load there will be more pellets in 6 shot than in 4 shot. For lead type shot in a 1 1/4 ounce load, there are basically 281 size 6 shot pellets and 169 size 4 shot pellets.
Actual recoil is determined by the payload (ounce of shot) and the speed at which the payload is traveling (feet per second, or fps). If those two are the same it doesn't matter if its from a 20 or 12 or even a 28, 16, or 10 gauge gun. That's just physics.
Felt recoil is a little different. That can be less or more depending on several things:
The weight of the gun. A heavier gun will have less felt recoil.
The action type of the gun. A gas operated semi-auto can absorb some of the recoil.
The fit of the gun to the shooter. An awkwardly fitting gun can have more felt recoil.
The position you are shooting from. Standing is better than sitting. Shooting extreme right or left can also make recoil feel worse (not all turkeys come in and stand right in front of us
even though that's how we picture them) .
Also a good recoil pad can dampen felt recoil.