I pulled the recoil pad and found it to already be, apparently, foam filled. It sounded far to hollow for that, though. The foam was very spongy. I started digging into it, finding that it only went in about 3". I dug it out and filled the entire hollow portion of the stock with spray foam. There is negligible weight penalty (.6 oz), which takes the stock exactly to its advertised weight of 21 oz.
Weights:
As shipped - 20.4 oz
w/o recoil pad - 18.1 oz
w/ new foam and no recoil pad - 18.7 oz
FWIW, my factory T3X stock weighs 27.3 oz. That's an expensive six ounces but I don't have to carry a plastic stock, regardless of how good that plastic stock is.