I just bought a unfilled caldwell rear bag and was wondering what the best filler would be for my needs. I shoot off of a harris front bi-pod in the front and mostly shoot off a bench but occasionally shoot prone. Weight doesn't matter as long as the bag can support it. I'm very new to long range and was just wondering what everyone else recommends. I've searched and saw where people use sand, lead shot, kitty litter, air-soft balls, rice, and so on. Thanks in advance for the help.