Scopes mechanical zero

[Stevanda]

Hi all,
I have been read that a scope should be set to its mechanical zero prior to being mounted.As I understand it by winding half way between the top and bottom of it's turrets travel.This would mean you would be limited to only a theoretical half of the available MOA.Not a problem with my NF scope and 20 MOA base but is this zeroing needed.I'm trying to get my head around this before putting the scope on.All comments very welcome.

 

[LouBoyd]

I like to start by zeroing a scope, not by counting clicks from each end of their range but by putting the scope on a box with two V grooves cut in the top and rotating the scope while watching a moderately distant object, then adjusting the knobs so the cross hairs don't move on the background. That sets the line of sight though the cross hairs concentric with the tube of the scope. It's easy to get it to the nearest click which is adequate. Counting clicks from each end is NOT the same. Not all scopes have symmetrical adjustment range, particularly in elevation. I keep a wooden cigar box just for that purpose.

Then I mount the scope on the rifle, (with or without a wedge base) and don't change the knobs. When I take the rifle to zero it I calculate (most any ballistic program will do) what the scope setting should be and dial that in to the scopes knobs. It usually starts out close to expected zero. If it doesn't I stop and figure out why. It's a quick check that the rail and rings were installed correctly and that the rifle is shooting concentric with the action.

You don't have to do all that, but it doesn't take much extra effort and can save a lot of time trouble shooting a rifle later. It also can save a few shots initially getting on target. It's possible to miss a 50 yard target completely with a "long range" scope which isn't zeroed. How do I know that ;-)

 

[Eaglet]

stevanda,

If a bunch of things fall in place like a well constructed scope with precise turrets, base screw holes drilled in the right place of the action etc, after you center the scope the way you mentioned, the following numbers would put you pretty close:

 

[LouBoyd]

I have to disagree strongly with Eaglet's suggested "pretty close" values. His elevation and windage values are just to get you on target and being off doesn't matter. However, guessing at the scope's line of sight centerline over bore distance will cause significant errors in all subsequent drop calculations. Measure that spacing with the best accuracy you can. I'd recommend to no worse than 0.01".

 

[Eaglet]

I have to disagree strongly with Eaglet's suggested "pretty close" values. His elevation and windage values are just to get you on target and being off doesn't matter. However, guessing at the scope's line of sight centerline over bore distance will cause significant errors in all subsequent drop calculations. Measure that spacing with the best accuracy you can. I'd recommend to no worse than 0.01".

I would absolutely agree with you if my statements are leading people to believe that once they dial the given values they're done!!! But that's not the case; my intentions are to put you on target and after that you bring the POI in, you fine tune it. I suggest 25 yards originally and then after you know you won't be missing the target, move it out to 100 yards or what ever you feel confident with.

Because the values were calculated for 100 yards, expect to be about 1.0" low at 25 yards, 0.5" low at 50 yards and on at 100 yards.

Again, my calculated values are very accurate assuming we give the right info; but are only intended to put you on paper without any hassle. Will also give you an idea of how much available adjustment you'll have left. NOT INTENDED TO BE USED AND WITHOUT SHOOTING TO FINE TUNE TO GO HUNTING...

 

[Stevanda]

LouBoyd and Eaglet thanks so much for your advice on this.The pieces of the jigsaw are slowly coming together.This morning I put the NF onto a V cut box and slowly spun the scope and adjusted the turrets so that centre does not move , an interesting excersise on it's own.Next step will be to sight the rifle in this weekend and do some load development.I will report back later with what happens.Cheers,Stevanda - New Zealand.

 

[Dr. Vette]

Here's a much quicker way to optically center a scope using a mirror. It might take all of a minute if you're slow.

Optically Centering a Scope -