If you look close, you will find that the factory stock is flexing right at the front barrel nut and going back to the magazine cutout. This is the area that needs work. Bedding around the recoil lug, front action screw, and barrel nut will help. Some people have gone as far as epoxying sheet metal to the sides of the mag cutout in the stock, which does stiffen it. Some also put a rod down the entire length of the fore end.
Another thought on adding weight in the back: put the lead shot and epoxy mixed together in a plastic baggie. That way you can get it out if you ever need (or want) to. The epoxy will keep the shot from shifting.
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