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Optical Center / Mech. Center

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/04/2006 at 10:27
Lineman View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: February/04/2006
Location: United States
Status: Offline
Points: 1

Hello All,

This being my first post. I would like to say that I have enjoyed reading the post and response on here.

My question is what is the difference between OC and MC, ( I think I know,,,LOL) and how does this affect the mounting/accuracy of the weapon. I have always mounted a scope, bored sighted, and went to the range to fine tune it. Is this the correct way??? I am woking on a project now, that a SS 10x42 will be mounted which I will be purchasing next week. I would greatly appreciate any response, or advice from the board.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/05/2006 at 09:22
Dale Clifford View Drop Down
Optics Jedi Knight
Optics Jedi Knight


Joined: July/04/2004
Location: United States
Status: Offline
Points: 5087
An Optical center is were you get your glasses fixed. No just kidding. O.C. is where the center appears to the brain as preceived by the eye. Peep sights, 1x opical, dot sights will try to center the eye, sometimes it is the mechanical center . Something like a doctor dot or Eotech's mechanical center is different than the O.C. And of course there is the machiniest M.C. which is sometimes referred to as " on centers" . (ex. center-axis of a gun action and barrel in which case it is rarely the optical center and you can't trust it by looking at it).
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: February/05/2006 at 17:19
Infidel View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: July/24/2004
Location: United States
Status: Offline
Points: 7
With the scope in v-blocks, align the crosshairs with a distant point, then turn the scope in the v-blocks.  If the crosshairs wobble, if they move off the distant point, then adjust them until they do not move relative to the distant point when the scope is rotated around its axis.  That is what most people mounting scopes refer to as the "optical center".  That is, the crosshairs are aligned with the centerline of the optics.

Keeping track of the dials, turn the elevation knob until it stops.  Then turn it the other way until it stops.  Set it halfway between those stopping points.  Do the same with the windage knob.  That is what most people mounting scopes refer to as the "mechanical center".  That is, the adjustments are in the center of their (mechanical) range.

On a good scope, the two centers will more or less coincide.  Any significant misalignment of the "center"s can indicate a problem with the scope.

Your method is just fine.  There are other considerations that might come into play, though.  If it is possible to adjust the scope's point of aim using the mounts, so that it is boresighted with the crosshairs at their mechanical adjustment center, that's good.  The idea is to preserve the scope's interrnal adjustment range for field adjustments, and to have the internal parts aligned with and centered in the scope tube.  If the rifle is going to be used for long range target shooting, then it's nice to boresight it and then zero it at short range (~100 yards) with quite a bit of down elevation dialled in, e.g., 20 moa.  Then more of the scope's elevation adjustment range is avaiolable to use for field adjustments.  That usually requires a slanted mounting system.


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