I just confirmed that the ACOG TA11F (calibrated for .223) works great with a .308 16" AR10 shooting 147gr FMJ.
Someone once told me that a ACOG TA01NSN (which is calibrated for .223 62 gr M855 ammo) works great for a 16" AR10. Most people won't believe this because all the 3.5x and 4x ACOGs with .223 reticles, and flat-top mounts are calibrated for M855 ammo shooting out of a 14.5" Barrel (TA01NSN, TA11F, TA11H, TA31F, TA31RCN, etc).
After zeroing at 100 yards, I found out it was true, that you can use these .223 ACOGs for .308. I was accurately able to use the BDC of this ACOG all the way out to 550 yards. Only thing I had to play with today was the holdover for windage, but the BDC (elevation) was spot on all the way out to 550 yards.
This seemed to good to be true, so I plugged the numbers in a ballistic calculator... and found out that it does matches up pretty dang close between M855 and M80!
Here is the data I used for the ballistic calculator:
ACOG 2.7" over bore (both .223 and .308)
.304 BC for M855 (62gr .223) projectile
.391 BC for M80 (147 gr .308) projectile
2900 FPS for M855, velocity of M855 out of 14.5" barrel.
2680 FPS for M80, velocity of M80 ut of a 16" barrel.
The numbers on the ACOG are meter indicators and not yard indicators. Now using the ACOG TA-11F BDC (designed for M855 out of M4) for .308 NATO M80 ammo out of a 16" AR10, my BDC will be off as follows:
100 meters: dead on
200: 1/2 MOA too low (~1" too low)
300: 1/2 MOA too low (~1.5" too low)
400: 3/4 MOA too low (~3" too low)
500: 1/2 MOA too low (~2.5" too low)
600: dead on
700: 1/2 MOA too high (~3.5" too high)
800: 2 MOA too high (~16" too high)
As you can see it is almost dead on out to 700 meters. At 800 meters, all it takes is a little holdover (aim about a head length lower) and you will be right there!
I should add that TA11's are the best option for .308 because of the longer eye relief, and you will need the longer eye relief when shooting .308.
Here was the test gun:
The Cartmann-AR10-CQB-Mod-32-Marcus-Allen
(Began Life as an Armalite AR10, 16" Light Barrel). Gun as pictured with empty mag and no Silencer is 10 lbs. Silencer is just for show, I don't shoot this gun with a Silencer, makes gun to front heavy (and POI shifts 4" at 100 yards).
Lucky for me I had a light gun so I can easily go from one pretend-make-believe-cover-with-tiny-port to the next pretend-make-believe-cover-with-tiny-port. Also lucky for me I did not have a underside Bipod to impede my quick operator like movements.. Lastly, From here on Snipers Hide, I learned that you are not really that cool if you shoot mostly prone. So that means I am cool now one of the cool kids because I shot off hand through a tiny port!
Another cool thing, was lucky for me the target was directly in front of the port! Pretend battles are fun when the stars line up!!
Someone once told me that a ACOG TA01NSN (which is calibrated for .223 62 gr M855 ammo) works great for a 16" AR10. Most people won't believe this because all the 3.5x and 4x ACOGs with .223 reticles, and flat-top mounts are calibrated for M855 ammo shooting out of a 14.5" Barrel (TA01NSN, TA11F, TA11H, TA31F, TA31RCN, etc).
After zeroing at 100 yards, I found out it was true, that you can use these .223 ACOGs for .308. I was accurately able to use the BDC of this ACOG all the way out to 550 yards. Only thing I had to play with today was the holdover for windage, but the BDC (elevation) was spot on all the way out to 550 yards.
This seemed to good to be true, so I plugged the numbers in a ballistic calculator... and found out that it does matches up pretty dang close between M855 and M80!
Here is the data I used for the ballistic calculator:
ACOG 2.7" over bore (both .223 and .308)
.304 BC for M855 (62gr .223) projectile
.391 BC for M80 (147 gr .308) projectile
2900 FPS for M855, velocity of M855 out of 14.5" barrel.
2680 FPS for M80, velocity of M80 ut of a 16" barrel.
The numbers on the ACOG are meter indicators and not yard indicators. Now using the ACOG TA-11F BDC (designed for M855 out of M4) for .308 NATO M80 ammo out of a 16" AR10, my BDC will be off as follows:
100 meters: dead on
200: 1/2 MOA too low (~1" too low)
300: 1/2 MOA too low (~1.5" too low)
400: 3/4 MOA too low (~3" too low)
500: 1/2 MOA too low (~2.5" too low)
600: dead on
700: 1/2 MOA too high (~3.5" too high)
800: 2 MOA too high (~16" too high)
As you can see it is almost dead on out to 700 meters. At 800 meters, all it takes is a little holdover (aim about a head length lower) and you will be right there!
I should add that TA11's are the best option for .308 because of the longer eye relief, and you will need the longer eye relief when shooting .308.
Here was the test gun:
The Cartmann-AR10-CQB-Mod-32-Marcus-Allen
(Began Life as an Armalite AR10, 16" Light Barrel). Gun as pictured with empty mag and no Silencer is 10 lbs. Silencer is just for show, I don't shoot this gun with a Silencer, makes gun to front heavy (and POI shifts 4" at 100 yards).
Lucky for me I had a light gun so I can easily go from one pretend-make-believe-cover-with-tiny-port to the next pretend-make-believe-cover-with-tiny-port. Also lucky for me I did not have a underside Bipod to impede my quick operator like movements.. Lastly, From here on Snipers Hide, I learned that you are not really that cool if you shoot mostly prone. So that means I am cool now one of the cool kids because I shot off hand through a tiny port!
Another cool thing, was lucky for me the target was directly in front of the port! Pretend battles are fun when the stars line up!!
