The BEST way to reduce recoil is to:
Shoot the HEAVIEST gun with the LIGHTEST loads in a gun that FITS.
There are 2 types of recoil - actual, which is a math equation based on weight of the gun, mass and velocity of the payload
and perceived or felt, recoil which is based entirely on gun fit
If your gun doesn't fit, then adding gizmos and weight and springs will do nothing to stop the bruise to your cheek or shoulder.
All of the recoil pads, hydraulic/spring/air cushion devices do is spread the recoil pulse over a longer period of time (measured in milliseconds).
If you are going to only add weight to the buttstock, you will upset ANY semblance of balance unless you also add weight forward as in under the forearm
Which recoil are you trying to reduce?