Personally, I just don't like getting beat up while trying to have fun. No neck/back problems, just don't like to hurt after a day of shooting. Synthetic stocks are USUALLY hollow. I know some aren't... So I just add a couple pounds of #9 birdshot into the cavity in the butt. I take some thick foam and press down as far as I can get it toward the grip. Then I put one ziplock freezer bag inside another and leaving them open, I push them down into the stock with a dowel and try to spread them open inside the stock. A funnel is used to fill the bags and I tap it all down while it is filling. You can get a LOT of #9 in a small area. Seal the bags. Cover with a thin piece of foam and put the pad back on. Really easy to bring back to the original weight if you need to. I hunt normally off of stands that aren't more than 200 meters from the road, so I don't care how heavy it is. I even did this to my Tikka T3 Light .308. I bought it in case I get to go hunting for some of the game in the alps. I can make it from over 10 pounds to right at 7 in about 2 minutes.
ngh