Re: What do you use for rear support?
I have used and still do some of the various types of bags from store bought to socks filled with styrofoam beads, beans, rice, bird seed.......... most of which has been mentioned and each works well.
A couple of years ago I came up with the idea of using a short bi-pod mounted on my rear sling swivel stud and have found for me that it works better than anything else I have tried.
Mostly I use the Stoney Point Rapid Pivot bi-pod. The legs are not "fixed" so they can be spread further apart or squeezed closer together for elevation adjustments. They also have a very small base that attaches to the rifle and are easy to pop on and off. Oh, and very light weight.
When whitetail hunting and sitting in a deer stand I often have a bag on the shooting rail and use my Stoney Point shooting sticks under the rifle butt. This combination will get me "benchrest" steady sitting in a chair....... if no shooting rail is available a good camera tripod with a rest attached works great for the front rest.