I use sand as I want the stability of the extra weight. Rice and other light items do not give me the stability that I like. The sand I use is the very fine play sand to fill leather rests. If using something like old money bags, which I have used dozens of, make sure you double stitch the seams and triple stitching won't hurt, and I mean ALL the seams, not just the one open where you put in the sand. Go over all seams and use the finest stitch per inch your machine will do with the thread you use. Also, use a heavy thread, not your normal clothing thread. The thread I use is a black heavy thread #69. It will not break easily and takes a lot of abuse. Also, don't overfill the bags, you want them to settle around your firearm forming a cradle. Then when you are done, just use common since and don't leave them out in the rain. If they do get wet, set them up in front of a fan for a few days, turning them over ever 6-12 hours. You will get them dry long before the stitching or bag starts to rot or weaken.