stubbicat, any change in the amount or position of human mass behind a recoiling rifle or how that human grips the rifle will change where the muzzle axis points when the bullet exits. Shooting smallbore 22 rimfire slung up prone in a 100 yard match, move your front elbow left or right an inch and if that's the only difference from the previoius shot, watch the next one miss your point of aim.
It's grade school physics; think about it for a bit (while).
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master