Onward Allusion's comment:
Two people shooting the same gun can get two sets of consistent results because they may:
- hold the gun differently
- perceive recoil differently
I've shot on and coached long range rifle teams with both aperture front and rear, service rifle aperture at the rear and post up front and scoped rifles. When "hot gunning" a single rifle among all of us, we all had different zeros on its sights. Each man on the gun set the sights for his own zero when he went on the firing line. Sometimes there was as much as 1.5 MOA spread in windage and/or elevation across all four of us on the team with the same rifle and ammo.
Regarding Onward's last line:
- and yes, even see the target differently through a scope because of the way they are holding/resting it.
Several times, I've proved this is also a myth. Prove it to yourself, if you dare.
Putting a collimator in the muzzle for scope sights (whose eyepiece is focused on and parallax free on the reticule and objecive lens is focused on the target so it's parallax free on the reticule) or a false bullseye in front of the front sight for irons or aperture sights, then having folks adjust the W and E knobs to align the reticule or sights on the target ended up with everyone being within 1/4 MOA of each other. When they repeated the setup, they would be within 1/4 MOA of their last one. Had to prove this many times to folks who, like so many, think each of us humans look through sights (metallic or glass) different ways. People don't realize that the light from the target passing by or through the sights to the human eye doesn't change from person to person. The light doesn't know where it's going nor where it'll stop.