Adding weight to a stock will definitely reduce felt recoil. Lead is denser than sand, so you wouldn't need as much lead as sand to achieve the desired weight. Plus lead would be cleaner than sand. I don't think you would want to add more than about 1/2 pound of weight.
Plastic stocks may have voids in them that you could put the weight in, otherwise you would have to drill a hole. Usually the weight is added to the stock under the recoil pad.
Lead shot works well because it easily flows into any size hole. Once in the hole you can add some white wood glue to the lead to make it quiet, and it's not too difficult to remove if you later wanted to. Thick lead wire, like fishing weight, also works.
Like previously posted, better recoil pads, like a Limbsaver, will help reduce felt recoil.
There are also recoil reducers that can be installed inside your stock that will reduce recoil. These are either mechanical or mercury filled units, but maybe an equal amount of lead would work just as well.
I have used all of these (except sand) in various rifles and shotguns, and they have all worked.
Last edited by buffybr; 10-15-2014 at 05:13 AM.