GettoPhilosopher

04-20-2012, 9:59 AM

Ok guys, help me out here. I don't know if I'm missing something, if I screwed up my calculations, or what, but I can't for the life of me get the drops right for an ACOG. (I'm using JBM Ballistics)

According to the ACOG Chart (http://www.ar15.com/forums/t_3_18/229420_Bartholomew_Roberts__Big_ACOG_BDC_Chart.htm l), the TA11F is calibrated for a 62gr M855 round out of a 14.5" barrel with a sight height of 2.5".

However, later posts show that has changed, and it's now calibrated for a 20" barrel.

I called Trijicon to confirm. They gave me both the calibration data (3050fps, 62gr bullet, 20" barrel) AND the MOA drops of the reticle. They are as follows:

100: 0

200: -2 MOA

300: -4.4 MOA

400: -7.8 MOA

500: -12.6 MOA

600: -18.6 MOA

700: -26.4 MOA

800: -35.8 MOA

Problem is, when I plug in that data, I get totally different drop values.

100:-0.0 MOA

200:-1.4 MOA

300:-4.0 MOA

400:-7.4 MOA

500:-11.6 MOA

600:-16.9 MOA

700:-23.5 MOA

800:-31.7 MOA

On snipershide, someone posted even WEIRDER values:

100: 0 MOA

200: 1.5 MOA

300: 3.5 MOA

400: 6.6 MOA

500: 10.5 MOA

600: 15.1 MOA

700: 20.9 MOA

800: 28.0 MOA

I've tried it with my Android "Shooter" app as well, I get similar results to JBM. I've also tried varying the values (3100FPS, 3000FPS, 2970 FPS....2" sight height, 2.75", 3"....etc). I can't for the life of me make the drop values provided by Trijicon make any sense.

Help? Even if I just shrug and accept their drop values as accurate (which I do), if I don't know what I'm doing wrong I can't trust the values I get for my rifle/ammo.

According to the ACOG Chart (http://www.ar15.com/forums/t_3_18/229420_Bartholomew_Roberts__Big_ACOG_BDC_Chart.htm l), the TA11F is calibrated for a 62gr M855 round out of a 14.5" barrel with a sight height of 2.5".

However, later posts show that has changed, and it's now calibrated for a 20" barrel.

I called Trijicon to confirm. They gave me both the calibration data (3050fps, 62gr bullet, 20" barrel) AND the MOA drops of the reticle. They are as follows:

100: 0

200: -2 MOA

300: -4.4 MOA

400: -7.8 MOA

500: -12.6 MOA

600: -18.6 MOA

700: -26.4 MOA

800: -35.8 MOA

Problem is, when I plug in that data, I get totally different drop values.

100:-0.0 MOA

200:-1.4 MOA

300:-4.0 MOA

400:-7.4 MOA

500:-11.6 MOA

600:-16.9 MOA

700:-23.5 MOA

800:-31.7 MOA

On snipershide, someone posted even WEIRDER values:

100: 0 MOA

200: 1.5 MOA

300: 3.5 MOA

400: 6.6 MOA

500: 10.5 MOA

600: 15.1 MOA

700: 20.9 MOA

800: 28.0 MOA

I've tried it with my Android "Shooter" app as well, I get similar results to JBM. I've also tried varying the values (3100FPS, 3000FPS, 2970 FPS....2" sight height, 2.75", 3"....etc). I can't for the life of me make the drop values provided by Trijicon make any sense.

Help? Even if I just shrug and accept their drop values as accurate (which I do), if I don't know what I'm doing wrong I can't trust the values I get for my rifle/ammo.