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Discussion Starter · #1 ·
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 :D
 

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The Tip is 100m, under the tip is 200m, the lit post is 300m/25m, and others are marked. I'm not sure what zeroing your that sight at 50yds is going to get you other than a holdover/holdunder headache at almost all ranges over 300m. Just some advice.
 

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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 :D
...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...
 

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Discussion Starter · #4 ·
I have a 50yrd indoor range in my neighborhood. I will be shooting mostly 55 grain LC M193. My Sig 556 is a 16in barrel. So when I zero ACOG to my 556 at 50yrds, I will use the tip of the little post / 300/25yrd for POA/POI and then when I get to a 100YRD range I should be close Correct? I have the TA31RCO-M4 Acog
 

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Ripper said:
I have a 50yrd indoor range in my neighborhood. I will be shooting mostly 55 grain LC M193. My Sig 556 is a 16in barrel. So when I zero ACOG to my 556 at 50yrds, I will use the tip of the little post / 300/25yrd for POA/POI and then when I get to a 100YRD range I should be close Correct? I have the TA31RCO-M4 Acog
...Ripper

...please read my reply carefully...disregarding the last paragraph...this is the "correct" way to zero your Acog...ONLY IF...you can meet the conditions in paragraph two...the important thing is that you zero at 100 meters using the tip of the chevron...POA=POI...it doesn't matter how you get there...whether you start at 25 yards...50 yards etc...just so long that your final zero is POA=POI at 100 meters using the tip of the chevron as your aiming tool...then the BDC reticle will "half ass" work on man sized targets at range...`

...the last paragraph represents a more simple and practical mannor in which to zero a low powered optic...such as an Acog...for use under 300 yards...and retain close quarter and mid range effectiveness with almost all .223 / 5.56 ammunition fired from a 16 inch barreled carbine...

...it doesn't matter if you use the top of the post...or the tip of your chevron...as long as you use one or the other "consistently"...a near 50 yard zero will give you roughly a 200 "meter" far zero...and the trajectory of the bullet will not be more that +/- 2 inches from your line of sight up to about 250 "yards"...you essentually have a less that 2 MOA "point blank range" of about 250 yards...and ~ 2 MOA PBR out to ~ 300 yards...

...with a 50 yard zero...you will be roughly between 1 1/2 to 2 inches high at 100 yards...when using the same ammunition ! ...ie bullet weight and velosity...so you can adjust for elevation by dialing down your elevation ~ 5 clicks...on your Acog...3 clicks = ~1 inch @ 100 yards or roughly 1 MOA...make sense ???

...yes...when you zero @50 yards...and then shoot at 100 yards...you will be close as long as you use the same ammunition...having the same muzzle velosity...this usually also means the same bullet weight...otherwise you will print either more high or low due to barrel time...

...i have given you "two" different options to zero your Acog...the first requires that you strictly control the ammunition you fire in order to perserve the bullet drop compensation feature of the Acog's recticle...the primary variables being velosity and the projectiles ballistic coefficient...using the second method is a more practical method for most shooters...and allows you a far greater choice of ammunition...
 

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Hey Ullie, while we are on the subject. Do you know what the TA33G-H is calibrated too. I thought it was M193 out of a 20" and my ballistics for this 68 and 75 load set I have will work, but if it were calibrated to the M855 out of a 14.5" that would work much better. I have tried to contact Trijicon with no avail. Thanks again and the indicator inside the reticle is marked 5.56F if that helps at all.
 

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...i believe...but not 100 % certain...that it is calibrated for M855 out of a 14.5 inch barrel...especially considering that the horseshoe/dot is primarily a CQB reticle...

...Trijicon could do a better job in their retical specifications...and also in their operators manuals...a 100 meter zero using the dot over target doesn't give you your best PBR for CQB operations IMO...i'm guessing that's how Trijicon has you zero this particular Acog ???...
 

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Yeah the zeroing instructions are given as dot 100m, illuminated post 300/25m, and so on. No 200m holdover stadia line but it seems that holding in the middle of the dead space between the dot (100m) and the post 300m works well.
From my experience last week using 55gr federals @2742 fps and zeroed at 100m, 200m is almost at the post, 300m is 1/4 down from the post, and 400m is a 12" holdover. It actually works really well out to 400m with just enough magnification to hit a 12" square plate with great consistency.
I understood the philosophy of use for this optic before I purchased it and fully believe that it is the ultimate no nonsense, KISS principle, utility optic for medium sized targets. Its no precision optic as you said, one must understand its limitations before shelling out $900 dollars for one.
Thanks again Ullie.
 

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cheney said:
Yeah the zeroing instructions are given as dot 100m, illuminated post 300/25m, and so on. No 200m holdover stadia line but it seems that holding in the middle of the dead space between the dot (100m) and the post 300m works well.
...the "dead space" gives you your best point blank range for CQB applications out to ~300 "yards"...you could zero using the dot over target POA=POI @ 200 "meters"...this will give you an approxmate 50 "yard" near zero with most ammunition...and then see where she prints using the BDC with the ammunition "you" are using...your results will vary depending on muzzle velosity and the ballistic coefficient of the bullet...especially at longer ranges...

...just a heads up....the instructions should read...for the top of the illuminated post...33 meters / 300 meters...not 25 meters / 300 meters...
 

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Yeah you're right Ullie, my mistake.
On another note, I looked at my rail on the sig and the ACOG and my scope which are both mounted on Larue setups cant slightly to the left due to the rails not being completely true. They are not twisted or out of alignment, merely the rail itself does not seem to be the same dimensions as the other 3 M-15s I have looked at and tried the Larue mounts on. The question is whether you think this will make a difference if I'm only shooting out to 600yds and if SIG has actually made the new ones to correct spec. If they have fixed this problem and made proper rails I'll just have them send me a new one, but if they haven't do you know of any online shops that machine custom rails so I could have one made that is correct? Thanks again
 

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Sig just sent me a new one and seemed to know about that series of rifles having that problem. It makes sense given they were trying to crank them out as fast a possible. I don't really think I can blame them.
 
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