Aperture sighting - bench vs. sitting position

[Pucky Freak]

I inherited a sporterized Lee Enfield No. 4 Mk. 1 (.303 Br.) from my grandfather. It has an aftermarket dovetail front sight post, and original flip up rear aperature sights. I had a gunsmith boresight it, which roughly centered the front sight. Today I took it to the range and from the shooting bench using my range bag as a rest, my groups were about 14" left at 100 yards. I moved the front sight post to the extreme left (about 3/16") which resulted in perfect windage (which seemed odd, but I just went with it), approx 3 MOA groups and a 150 yard zero. Next I fired my last 3 rounds from a sitting position (no rest) and shot group was about 14" to the right at 100 yards. It would seem that the bore sight worked fine for sitting position, but not bench?? At this point I had run out of my grandpa's supply of handloads (they look like 180 gr.), so couldn't test any further. I realize the sample size from my last group is pretty limited.

Question - is there more likely a problem with my shooting form from the bench, or sitting? Anything else I might be missing? Suggestions?

With some of my other firearms (.22 with partridge sights, 12 ga. w/ 3-dot, slug gun w/ red dot, and .30-06 w/ crosshair scope), I haven't had this issue. I typically sight in from the bench, then confirm with seated with no rest, and finally awfulhand, to make sure the sight adjustments will work in hunting situations at appropriate yardages for each of the positions.

Also, any recommendation for factory rounds? I was looking at Hornady 150 gr, but maybe someone has had luck with something else. Obviously is not my primary hunting rifle, but I would like to punch at least 1 tag with my grandpa's trusty deer rifle, as a memory of him.

 

[Pucky Freak]

I just thought of one more thing, and maybe this is the critical factor? My last group of 3 shots from a sitting position my back was leaned up against a solid barrier. I've never shot like this before, but maybe the lack of give in my shoulder when the shot was fired threw off the windage. Then again, prone position makes for a very solid backstop, and to my knowledge this works to improve accuracy, not hurt it.

 

[SticksMcKinley]

I would think that your sight picture through the aperture and possibly your cheek weld is changing between positions, although handloads should always be questioned in such cases. I've seen similar sighting problems, but not necessarily to that extreme with iron sight shooters on ARs, Springfield types, etc. First thing I would suggest is dry practice at home with an EMPTY weapon and no ammunition present. You might not be able to re-create your bench position, but definitely work on standing, sitting and prone and focus on finding the same aperture picture every time. I would adjust my bench zero if my position zero was consistently different with known good ammo as it could be an optical variation. As I'm getting older, I'm more aware of these "optical variations." I also don't consider a rifle zeroed until it's been to the range a few times and run through different positions like you're doing. Wish I could recommend some .303, but don't have enough experience with that round to give you any.

Yes, I would expect varying recoil management could cause that shift, too.

 

[Pucky Freak]

I would think that your sight picture through the aperture and possibly your cheek weld is changing between positions

I bet you're right, especially if my eye relief is different due to inconsistent cheek weld. I do not have any recent experience shooing either an aperture sight or a monte carlo stock, so I've got a long way to go in developing a repeatable form with this gun.

You might not be able to re-create your bench position

I'll see if I can, then carry over checkweld to the other positions w/ no ammo. If it doesn't work, I'm thinking I might give up on the bench position as my basis for the other shooting positions.

Thanks for the advice