Originally Posted by
militarymoron
the utility of a 'absolute/true' co-witness, IMHO, is as a sanity check to see if anything has shifted, or checking that you optic is still zeroed when you remove and replace it. the dot doesn't have to be co-zero'd with the irons to do that - you can zero the dot independantly, then check to see where it is in relation to the front sight when looking through the irons (windage should be centered, but you can be 'one dot width' above the FSP, etc).
normally, you'd never look through the irons when using the dot. i agree - it defeats the purpose. however, there have been instances where i HAVE utilized the rear aperture with the dot to sharpen it up. the sharpness of the dot depends mostly on your vision. my eyesight isn't that good, and using the small rear aperture when sighting in the dot, or for longer ranges on small targets acts like almost like a pinhole camera and sharpens up a dot that might appear a bit blur or fuzzy. for those with less than perfect vision, look at your dot, then flip up the rear sight with the small apreture and look through it again. chances are you'll see a sharper, more distinct dot.
i think the point of brett's original post was to try to get some agreement/standardization on the terms used. here are my suggestions for defining the terms:
Co-witness - the ability to view the irons sights through the tube. This applies to any height of the optic relative to the irons, as long as they can be seen. the dot can be adjusted to the irons or zero'd independantly.
Co-zero'd - i suggest discarding the terms 'absolute' or 'true' co-witness as they're confusing. this is when the dot is adjusted so it sits on top of the FSP when looking through the irons. the zero will only be valid for the distance they're both zero'd at.
I sat back and thought about this over the weekend over many, many pints of Guinness and using the term "Co-Zero", if your BUIS or Sight already sit in thee bottom 1/3 of your Optic / Red Dot, and your BZO your Optic /Red Dot @ 25m, and then adjust your Sights to it, your will not have a correct 300m BZO. Or even the other way around.
Lets just say that you sight in your Optic / Red Dot @ 25m and then adjust your Irons to them. Well then look at the setting on your elevation, it will be way blown out due to the fact that you (from the start with your lower 1/3 co-witness) have a gross adjustment of coming up at .25" or more. Then after your Rear is at the correct level, bringing your front sight post up to Co-Zero would be almost to the point of your Front Sight Post and Detent coming out or damn close to it.
IF your sights are on the same level with a Co-Axis with the plan of each being the same plan, it would be close or if not perfect for the idea of Co-Zero to work.
And going back to another question that was brought up earlier (sorry for hi-jacking my own thread). There is DIFFERENT POA/POI for different Optics / Red Dots with many variables in place, ammo types, optics, bbl lengths, etc. Example: Say you sight a EOTech in @ 25m (and the offset is 1.25 low) and your think that your POA/POI in Center mass of the Black Dot or Circle and your zero it to that. Then push your 25m BZO to 300m and see what happens. IF you were at center mass on that @ 300m your will be aprox. 15” High, and that is in perfect conditions taking out all accountable errors, IE MOA of ammo and the aprox 1 MOA for shooter added to the MOA of the gun. In all reality your could be pushing to a extreme of almost 30” off your center mass BZO @ 25m. Hope that makes sense !
B
Brett W
Elite Defense
Vice President of Domestic Sales and Marketing
FN Senior Manager of Assault Weapons - SCAR Program 2006-2010
Former Troy Industries Inc Director of Operations 2003-2006
Each Warrior wants to leave the mark of his will, his signature, on important acts he touches. This is not the voice of ego but of the human spirit, rising up and declaring that it has something to contribute to the solution of the hardest problems, no matter how vexing!
-Pat Riley
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