Impact M3 Scope Rail Alignment

I always optically centered my scope and remounted it to the rail. I would then use the slop in the rail fit to get it as close to the vertical plane as I could before torquing it down.
Preinstall the screws in the rail, and stop just short of snug. Remount scope and center the set up before tightening.

Center up on paper, using the rail like windage adjustment.
 
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I always optically centered my scope and remounted it to the rail. I would then use the slop in the rail fit to get it as close to the vertical plane as I could before torquing it down.
Preinstall the screws in the rail, and stop just short of snug. Remount scope and center the set up before tightening.

Center up on paper, using the rail like windage adjustment.
I do this too.
Aligning the edges of the rail perfectly to the spine of the gun always resulted in needing at least 3 mil of adjustment to the left on my 700mm mk2.
I initially blamed the barrel system but as soon as I switched out to a backbone everything just lined up near perfectly, with one click required to get windage dead center. So there must be a touch misalignment in the rail machining over and above that bit of slop in the attachment, at least in mine.
My pellet shooting m3 still has its OEM rail and spine and needed similar adjustment.
 
I do this too.
Aligning the edges of the rail perfectly to the spine of the gun always resulted in needing at least 3 mil of adjustment to the left on my 700mm mk2.
I initially blamed the barrel system but as soon as I switched out to a backbone everything just lined up near perfectly, with one click required to get windage dead center. So there must be a touch misalignment in the rail machining over and above that bit of slop in the attachment, at least in mine.
My pellet shooting m3 still has its OEM rail and spine and needed similar adjustment.
My experience as well, before and after adding a new backbone.

Patrick
 
I am saying this is normal tuning procedure ... from a mechanical engineering perspective. In the rail it was a designed freedom of motion that you can adjust L-R the scope, in contrast to a backbone rail.
Imagine this - and sooner or later you will get to that stage to realize....
Let say you zero sighted in your scope at 50 yards/meters... also meaning the scope is in optical centerline...
Next will be - shoot a 20 y/m and 100 y/m (without moving anything on the scope turrets) and you want to hit a same vertical centerline at both 20 and 100 ... you may need to go there and back several times until you center the rail.
With a backbone rail you got what it is machined in the rail = no adjustments... if the machining was off you are screwed...