Scope Adjustments; Zeroing and Limits

[Bart B.]

Took my two Weaver Model T’s to lay in mounts with loosened top clamps, then spun them until reticule’s stayed at the same place on target at short range; that’s mechanical and optical zero (M/O zero) for the scope as the erector tube’s optics are centered in the scope tube. Both started out making a circle several MOA in diameter, but ended up with about a 1 MOA error from perfect. Blamed that small error on the tiny out of round and clearance to spin the scope tubes are spaced only about 3 inches apart. Both scope tubes are very straight; no evidence of being bent.

Loosened knob set screws then put both at zero; tightened set screws. Then moved both knobs to their limits from M/O zero looking through the scope verifying the reticle moved with each click. Here’s the results:

Weaver T10 bumped up to 16X;
...elevation - down 27 MOA, up 60 MOA; 87 MOA total range.
...windage - left 30 MOA, right 43 MOA; 73 MOA total range.

Weaver T16;
...elevation - down 11 MOA, up 60 MOA; 71 MOA total range.
...windage - left 26 MOA, right 46 MOA; 72 MOA total range.

Both have less adjustment range left and down from M/O zero. Most towards the adjustment knobs; right for windage and up for elevation. Proof to me that half way between the knob's mechanical limits is not M/O zero on these scopes; a popular belief amongst rifle shooters for all scopes.

Do your own tests with your scopes; if you wish.

 

[jmr40]

If using windage adjustable mounts this is important. With other mounting systems it might be interesting to know, but far less important.

 

[Bart B.]

If you've zeroed the scope before you mount it, when you bore sight the rifle with that scope, you'll soon learn how far off the receiver/scope-mount axis is off the bore axis. If it's the wrong direction quite a bit, you'll have only a few MOA of adjustments typically in windage. So I learned years ago bore sighting a Ruger 77 to a Redfield 3-9X scope.

 

[Laphroaig]

Many people badmouth the old Redfield/Leupold dovetail mounts, but their rear windage adjustment capability allows you to mechanically align the bases with the bore in the initial stages of sighting in. Your scope will be close to optical zero from the start.

The downfall, of course is that only the front ring holds the scope against recoil. I've had quite a few on 30-06 and other popular calibers and have never had an issue.

Laphroaig