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New mount - Factory zero windage

Printed From: OpticsTalk by SWFA, Inc.
Category: Scopes
Forum Name: Target
Forum Description: Paper punchin' scopes
Printed Date: July/20/2018 at 01:53
Software Version: Web Wiz Forums 11.10 -

Topic: New mount - Factory zero windage
Posted By: mtstream
Subject: New mount - Factory zero windage
Date Posted: July/28/2014 at 12:05

I'm mounting a Vortex Viper PST on an M1A EBR using the Sage DCSB and Vortex low rings.  After leveling the rifle and scope I also hung a plumb line at about 20 yards (farthest line of sight points in my house) - everything lines up.

I then dropped in a sightmark laser bore sight and noticed it was a full 1MOA left.  Does this indicate that my scope is not centered to the bore right to left?

I turned the windage knob until it stopped, counted the clicks until it stopped the other direction = 282.  At 4 clicks per MOA that would equal 70.5MOA of adjustment as opposed to the 65 advertised.  Counting back to the 1/2 way point is 141 clicks.  Should this be considered the true centerpoint of the scope or should it be the factory zero?

I want to ensure there's not some point of error introduced through the mounting - in other words I don't want to have to make windage adjustments as well as elevation adjustments when changing distances.


Posted By: 8shots
Date Posted: July/29/2014 at 01:39
Yes, your scope is not centered to the bore.
However 1MOA is very little and not worth worrying about. Of course a lot depends on how accurately you set everything up (plumline, rifle, laser bore etc)
The best way is to take the puppy out to the range and shoot a shot out to 100yds and see where the bullet impacts in relationship to your aimpoint.
Mostly it is expected to be 3 to 4 inches off. Don't sweat it, just dial in your correction and you are good to go.
If your scope was set up level to your rifle, your windage will not move with elevation adjustments.

Posted By: Ericbc7
Date Posted: July/29/2014 at 20:40
Do you mean the lazer was 1/5 inch left of the crosshairs ( corresponding to 1 moa @ 20 yds) or 1 inch @ 20 yards?
How confident are you that the lazer is true?
Good luck

Posted By: mtstream
Date Posted: July/30/2014 at 11:09

Unfortunately, my laser batteries died so I can't recheck until I find some more.  I had just about become convinced that it was the factory zero not being the center of the scope until 8shots post.  If I knew for a fact that the scope was perfectly parallel to the bore just slightly off to one side but still parallel, then it wouldn't be much of a concern.  But if the cause was due to a slight angle in the scope then it would amplify at further distances and that adjustment would need to be taken into account with elevation changes.

Ericbc - the dot was on the 1MOA mark in the reticle.  I don't know that the laser is true - its the cartridge version that goes into the breach.  I would think if it was off it would hit the barrel (22") but don't have a lot of experience with them.

Posted By: 8shots
Date Posted: July/31/2014 at 01:22

Don't sweat the small things too much.

I have a rig set up that I did just with a plumb line and rifle rest. Out to 660yds it dials elevation correctly without effecting windage.
There is so much other factors at long range that windage creep due to a slight off vertical set-up is not a major issue.
Wind, atmospheric conditions, rifle accuracy etc all play a major part on achieving a first shot hit.
What distance are you looking to shoot at?

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