I've used several of them in several different O/U's. I finally concluded a chunk of lead weighing the same amount accomplishes just as much recoil reduction/absorbtion. I like the lead better because it is shorter, which keeps the weight forward and does not make the gun butt-heavy, and because you don't hear the sloshing of the liquid. I make my own lead dowells in various sizes to fit various stock-bolt holes.
HOWEVER, I am removing or at least greatly reducing ALL such weights these days and just shooting lighter loads instead, as the reduction in recoil is vastly more than what you get by putting even a big weight in the gun.
