Read the sticky on adding weight to the fore arm.
Here are the several way's I've added weight to different stocks.
Mix the shot with epoxy, then pour/tamp it into a hole in the stock.
Mix the shot with epoxy, then pour/tamp it into a piece of pvc pipe, THEN, put it into the stock hole and epoxy a snug fitting plug filling the hole to the base of the stock. I guarantee it won't shift in any way.
Do the same thing but use a piece of black pipe cut to fit, plus the epoxy/shot mix and wood plug.
Do the same thing but use a piece of alum tubing slightly smaller than the hole in the stock. Put a delrin plug over the stock bolt head, then the alum tube, then a delrin "shock absorber" between the alum tube and the recoil pad and an extra screw close to the bolt hole.
Do similar things but use expanding foam to keep the pieces and parts in place...usually done in hollow synthetic stocks.
Use one of the cheap mercury recoil reducers in the buttstock and one of the "pencil" type epoxied in a slot in the forend.
Put the shot in a plastic baggy and stuff it into the stock hole...usually done temorarily to adjust the shot load to find the "perfect" amount of weight...but sometimes it gets to be a permanent "fix" when I get lazy.
Leave off the plastic baggie, pour the shot in the hole and fill it with expanding foam, screw the recoil pad on rapidly leaving one screw slightly loose to let the foad expand out through the crack.
After solidifying, trim the excess foam off the stock face and recoil pad...really works great and is easy to remove if you (I) can't make up your(my) mind.
Calculate the amount of lead required, melt and pour into a piece of black pipe, alum tubing...follow the different ways of stuffing it into the stock hole and holding it there.
Buy some 1/4" round fishing lead weights, weigh out the requred amount, fold to fit the hole, foam it in or epoxy it in, or pound it in, or just use a snug wood plug tamped into the stock hole, cut flush with the stock face.
....Or any combination of the above that provides the requred weight, is cheap and might work.
As long as the weight doesn't shift and the stock is held on tight, it won't split the stock.
Oh...and some attempts I'm way to embarrased to talk about.
'Njoy
....Or get tired of the whole thing and get used to the slap or give it to a smith to mess with, it might be cheaper in the long run and less hair pulling or in my case (no hair) skin scratching.
The road to success if full of potholes, giant deep chasms, ant hills and tall mountains and is littered with broken dreams and promises, AND many, many small and large satisfying wins.