If you lay a revolver barrel on a sandbag there are two problems: 1. You may blow a hole in the bag with muzzle blast (if it is a big bag) 2. The revolver does not recoil the same and will give a different point of impact.
If you want to attain the same identical point of impact (not always necessary) use the cup and saucer grip and lay your hand on the bag, pressing in to a deep indent. You will get good support.
On the other hand, it would not take much work to build yourself a heavily padded V notch support that you can lay the barrel in, portable enough to take to the range. With this kind of rest you seat the butt in a sand bag, rest the barrel in the notch and bear downward to keep contact as you fire a string. I used a rig like this for years before I could buy a Ransom. It worked.