IVe got a Crosman Raven "youth" riufle with a synth stock....
stuffed it full of plastic grocery bags to thepoint of nothing else can fit and its very dense.....
it helps, but that stuffing that stock now makes me think that the quality of the stock is gonna really affect how well filling it with anything is gonna work. I also filled amany of the little "compartments" in the forend of the stock with stick on foam. Again, stuffing and filling helps, but IMO some stocks wont respond as well as others ....
The raven is a fun gun BTW....