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1/10/2009 7:22:25 PM EDT
Greetings,

I finally received my ACOG TA01 back from some factory warranty issues.  I installed the TA51 mount and the Troy BUIS by recommendation (I'm glad I did, what a great little sight), and took it out immediately and got sighted in at 25 yards.  As I moved to the 100 yard range, I realized that my projectile P.O.I. was about 4-5 inches high.  I moved back and forth between the 2 distances to ensure it was not mechanical error, and started to notice the front muzzle flip of the rifle.  I think this was causing the issue, but only at 100 yards.  As I began compensating 4 or 5 inches low, I started getting nice little 1.5 and 2 inch groups.  What is my fundamental issue?  I use a tapco vert grip and shoot from the bench.  Is there something in my form I am missing?  Thanks in advance...

1/10/2009 7:42:09 PM EDT
[#1]
A 25 yard point of aim=point of impact zero is a terrible zero for most practical purposes for an AR-15.  Your shots impacting high at 100 yards have nothing to do with "muzzle flip"; it's simply a matter of the trajectory of the 25 yard zero.




1/10/2009 8:10:56 PM EDT
[#2]
I didn't think so with the lighter rifles but couldn't rule it out because of my lack of experience.  So the best zero is 100?  Any good links on studying 5.56 trajectory/ballistics to cure my ignorance? I appreciate it.
1/10/2009 9:08:14 PM EDT
[#3]
For .223, your best zero is at 50y.

http://www.ar15.com/forums/topic.html?b=3&f=18&t=328143

Having said that, I think the ACOG manual states that you should use a 100y zero so the BDC lines will be accurate.  So, double check that manual.
1/10/2009 11:11:34 PM EDT
[#4]
Quoted:
For .223, your best zero is at 50y.

http://www.ar15.com/forums/topic.html?b=3&f=18&t=328143

Having said that, I think the ACOG manual states that you should use a 100y zero so the BDC lines will be accurate.  So, double check that manual.




Yes the ACOG zero is 100 yards. What is painful is that nearly everyone in the Army with an ACOG is forced to zero on the 25M line....Makes the sight way the hell off at the ranges the ACOG is good for...

1/11/2009 7:24:34 AM EDT
[#5]
Thanks for all the good points and info gentleman.  I am ready to re- zero now.  The manual does state that the 25 yard zero makes it also zeroed at 300, but 100 is best.  I learned some new things today about my optic. Have a great week!
1/11/2009 9:23:53 AM EDT
[#6]
Wow hell thanks for that pic.  I knew it worked that way but didn't realize how much BETTER the 50 was.  25 and 100 are useless, not just "not quite as good".  Wow!

Centertop- I applaud you on your correct use of "ensure".  
1/11/2009 10:02:18 AM EDT
[#7]
Yes the ACOG "should" be zeroed at 100 yards so the resident BDC markings will be correct, however, if you only have a 25 yard range to zero your ACOG here is what you do.  Set POI 1.75" lower then POA and you will be almost dead on at 100 yards.  That is with using 55 to 62 gr. 5.56 ammunition out of a 14.5" or 16" bbl.

MadDog
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