I have a TA11 on a TA51 mount then on an ARMS Swan Sleeve.  A while back, I tried sighting in the TA11 at 100 yards. No matter what adjustments I made, all of my shots were hitting about 3" - 6" high at 100 yards.  I must have gone through 100 rounds trying to get it to shoot lower but top no avail.  

I sent the ACOG back to Trijicon and about 4 weeks later, it was returned to me.  I just got back from the range today and I am having the exact same problem.  I cannot get the ACOG to shoot any lower than 3" - 6" high at 100 yards.  I was using Winchester white box 55gr ammo as I was told they were calibrated for 55gr.

I have sighted in rifle scopes before but I have never seen anything like this before.  I appreciate any help you can give.

Thanks

Have you checked your mounts (both ACOG to TA51 and TA51 to receiver) to verify that they are secure and not working loose?

i had a similar problem once, i had the back end of the scope sitting on top of the ARMS flip up metal bracket on the ARMS 38 sleeve.