I decided to split the two types into different post to keep them from getting too windy.
Precision shooting is a bit different then position shooting. Disputes between the two type shooters are as common as 9mm vs. 45 or AK vs AR feuds.
Both work but work for different style of shooting. Being a High Power and Small Bore Shooter I'm more versed on position shooting where the sling is used un-supported but I'll take a stab at precision shooting in the prone position.
Again, I can't stress enough about being relaxed.
In precision prone, the body is straight behind the rifle, If one was to draw a line from the barrel it should extend down the back bone to the center of the butt.
The shoulders should be intersect the rifle at right angles. If you were to lay out the shooting mat, and draw a line down the middle, (head to toe), that's where the body should lay. Now if you were to draw a line forming a cross on the mat, that is where your shoulder and elbows go.
In precision, you don't hold the rifle at all, the front is resting on bi-pod or sandbag. The butt rest on the rear bag. Again the right hand holds the pistol grip only firm enough to support the hand on the stock so as not to disturb the NPA when squeezing the trigger.
Again the head is relaxed and resting on the butt of the rifle.
I can't stress enough that you need to be straight behind the rifle. To the point if there is any muzzle jump to the left or right upon firing, you're not straight. You shooting hand should be able to come away from the gun to change magazines, reload the rifle, write in your data book, without disturbing your natural point of aim.
Again the head needs to remain straight, bring the rifle to the head, not the head to the rifle.
This is true in any position, standing, prone, kneeling, or setting. Its also true with pistols and revolvers.
Remember, RELAX. There is no reason, regardless of age, one could get cramped up in prone or any other position.
Make sure all your shooting equipment is in reach so you don't have to disturb your position to do any of the activities you do while shooting.
I'm basically a lazy person. I don't want to use my muscles any more then I have to so I don't, therefore I don't get cramped or sore while shooting.
I realize its hard to understand what I'm trying to put forward from just reading (especially reading what I write). A good coach in invaluable.
I'd highly recommend attending a CMP GSM Clinic taught by Master Instructors regardless of which style of shooting you choose. Explain to the instructor any problems you may have and he'll work out a position that works for you. No two people are built the same, each position need to be adjusted to the individual shooter, this is where a good coach comes in.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071