Ripper said:
Want to Zero my ACOG TA31RCO At 50 yards. which position on the cheveron do I use? Is it the tip of the small post under the 200 meter part of the cheveron? Pictures would help. Thanks
...the ACOG TA31RCO-M4CP's reticle is calibrated for M855 ammunition out of a 14.5 inch barrel under standard atmospheric conditions @ 1000 AMSL...any deviation from this...especially a longer barrel and/or ammunition with different BCs and muzzle velosities will cause strike errors...the greater the range...the greater the error...
...that said
...the correct way to zero this particular Acog AND perserve the BDC calibrations when mounted on your 556 is to use ammunition as close to the M855 when fired out of a 14.5 inch barrel in velosity and having a similiar ballistic coefficient...somewhere around .300 (M855 has a BC of ~ .304)
...your final zero should be with the top of the chevron POA=POI at 100 "meters"...how you arrive at that doesn't matter...
...you can shoot POA=POI using the "top of the chevron" @ 50 yards and adjust and confirm @ 100 "meters" ...you'll need to go down about 6 or so clicks in elevation...
...the top of the chevron should be your 100 meter zero...top of the post your 300 meter zero with a close in zero of about 33+/- meters...the top point inside of the chevron 200 meters...line 4...400 meters and so on...anything past 400 meters is pretty optomistic IMO...
...the Acog is not meant to be a precision optic..the Acog was designed to hit man sized targets at range...it is not designed for precision shooting...and at best will get you on target based on statistal averages of size...and the relationship between velosity and distance to target...determining time of flight verses the acceleration of gravity...and so on...
...considering the Acog's limitations...and the differences in barrel length of your 556 and the ammunition you'll be "primarily" shooting...i would zero POA=POI @ 50 yards using the top of the post and the ammunition you'll be primarily using...or the top of the chevron...whichever you perfer...and call it a day...confirm that you have a 200 meter zero...and shoot POA=POI out to 250 yards with a slight holdover at 300 yards of ~ 6+ inches or so...my thoughts anyway...