Neither have I. In the Marines I was issued a "day pack" (glorified back pack) or what we called a "war bag" War bag being a reverence to an overnight bag you kept in your car in case one of the nice younge ladies of southern California decided to invite you over for the evening. We called them "war bags" because our SgtMaj would always end his safety briefs with "If you go to war this weekend wear your flak and kevlar" IE prophylactics.Wow - this thread has been going since '07!
No - I seldom support the buttstock with anything but my shoulder. Up front I might use a bipod or shooting sticks. More likely to just rest it on my pack, or a rolled up jacket, or believe it or not, just use the shooting sling wrapped snug around my arm. All have worked for me.
Depends on the time & natural rests available. Made a 400 yard shot in Wyoming, using a very handy tree limb, while standing. Worked great. My pard actually snapped a photo of me using the rest. I had just dropped the deer, and was waiting, ready to place another shot if necessary. It wasn't. The deer is just above that line of bright, bright morning sunshine and can't be seen:
For ultimate accuracy, of course nothing beats a good solid rest. I just don't usually find a benchrest in the field. Odd...
Now that I am older and wiser and married the 'ol war bag gets used to hold my rifle data book, ammo and cold weather gear as well as camel back. My heavy sweater makes for and awesome field expedient rest for the back of my Mcmillan A5 stock and Harris bi-pod up front.