I have an Armalite AR10 with a 20" barrel and flattop upper. I have a TA11C ACOG for it. I know that the TA11C is made for a carry handle mount, but the ACOG FAQ says that if I sight it in 0.7" high at 100 yards (meters?) on a flattop that all the ranging marks will be within 0.5" out to 600. Pretty damn close for me. According to Trijicon, the TA11C is calibrated using 168gr BH at a muzzle velocity of 2500 fps. I forgot to ask what the height above bore is that they use with the carry handle, or if it is in yards or meters.
Okay, this is where it gets difficult: I want to use M80 Ball or equivalent (Winchester white box, South African, or any kind of 7.62 NATO 147-150gr FMJ) to sight in my ACOG, as I can't afford a steady diet of Black Hills 168gr Match ammo. I know that the NATO type, 147-150gr stuff will have some variances, but they should all be in the ballpark of each other minute-of-ACOG-wise. Having all the data from Trijicon except the height over bore and the yards/meters thing for the 168gr BH, I want to figure out what my drops and holdovers from the etched lines on the ACOG will be for the NATO FMJ stuff.
Obviously the reticle can still be used for rangefinding, but I am assuming I'll need to know what the drop in inches at the various ranges will be for 168gr BH (hence the hashmarks), and then compare to the drop in inches for the NATO FMJ rounds. In other words, if the stadia line indicates a target at 500 yards (meters) on the TA11C then how far under/over the established stadia line should I hold for the NATO FMJ ammo?
The missing parts of the equation are the yards/meters measurement and the height over bore measurements for the carry handle and the flattop. Or will they even matter? I'm thinking that if I use the data and sight-in point of aim (top of the donut at 100 whatever) with the NATO stuff then all I need to know is the drops at the various ranges of the BH 168gr to guesstimate holdovers/under.
Hope this isn't too confusing....