The powder charge and wad weight are part of the calculation for free recoil since they exit the muzzle. However, they are inconsequential compared to the shot charge and gun weight and muzzle velocity.
The shells you questioned have nearly 20% more recoil than a standard 7/8 load at 1200. Twenty foot pounds of recoil is substantial. It will thump with authority. Take everyone's advice and leave the 3" shells in the store.
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