I use a Buddy Bag front, sometimes with an extra handmade sandbag ( 5x5) with it to help adjust height. I use a rabbit ear leather sand bag. I put my left hand on the scope of heavy kickers and hold tight. With lighter rifles, usually just put my fingertips on the top edge of forearm. I workup loads with 3 shots. If I find one I like, I then will shoot five, but wait a few minutes between each shot. I start each load with a cold barrel, i.e as in hunting. Sometimes, I find five shots reveal a loser. If I'm satisfied, then I try it further out. To "verify drop", I have a spot out in the desert. I put the Buddy bag on the corner of the truck/tailgate (closed) and my right elbow on the truck side. I then measure the drop, put a piece of tape around my group, go back and see where the group is in relation to my crosshair and top of duplex post ( Love a Duplex!) at 400 and 500, I use the power setting to superimpose the top of the post with the group. I then practice over the next few months, from hunting positions. All this takes time, of course. But this works for me, someone else may not get the same results, I don't know. I just know that, for me, 350 to 400yds is really challenging, from hunting positions. I much prefer to kill game under 250...the closer the better.
Oh yeah, I hate Bipods, I use a lwt set of shooting sticks from the sit if need be. I like the kind that fold up? My father taught me that a "good rifleman" knows how to find/use "a good rest". Field expediency to me means get still, someway, somehow but always to
"take your time in a hurry".
