I have done several in my younger days. It is interesting to say the least.
make small pours, wrap a wet cloth round the stock. Pour no more than 1", in hard walnut, and that may catch on fire. Do not put water on molten lead as it will explode all over you and the ceiling. I had to throw one Birch stock in the swimming pool. In another 40x stock, the lead just burned a hole in some soft grain and came out just behind the pistol grip, it looked like Silver inlay.
Count on very darkened stock with no finish(no kidding!!!!) You can call it dark Burl.
If you don't like all the above, then make very small pours with molten lead, and don't do it with your buddies watching, because will urge you to,"go for it".
The smart move would be to buy lead wool or #9 or 12 shot if you can find it, and mix the lead shot in casting resin. Don't pour over 2" at a time of the casting resin either, as it puts out some serious heat, you can crack a stock.
#12 shot
https://www.ballisticproducts.com/Chilled-Lead-Shot-12-13mm-10_bag/productinfo/02612/
Lead wool
https://www.homedepot.com/p/5-lb-Lead-Wool-B13652/202246295
In stock?
Mix with casting resin, tap down with a wood dowel, flat on one end.
In the late 70's, we got serious about being able to see our hits on p. dogs, and reducing the beating we were getting from recoil. We made a flat fixture that went from the front tang screw to the front sling swivel, and attached a diver's weight that weighed 9 lbs, maybe 12, it did the job!