Before I start this may or may not work for you. Use this information at your own risk. So I have long struggled with my Benjamin summit being too muzzle heavy. I love the gun this was my one issue so I corrected the weight today. I discovered the rear of the stock was hollow so I tried a Phillips head to remove the buttpad it unscrewed easily and behold an empty cavity. So how to fill it? well I needed something that would fill all the gaps. I went to the local Ace got some inexpensive 25 year acrylic latex caulk tubes and a caulk gun and filled the stock with caulk cleaned it up and put the butt pad on resealing the compartment. It worked well for me but again ymmv.