ACOG BDC reticle measurements

[StainlessSlide]

I've been shooting some ACOG optics at the actual ranges indicated on the BDC (it's important to remember that these are meters). At the altitudes I shoot at, the longer range marks are significantly off, but it is possble to find factory loads that match pretty well. Of course, handloads can also be calibrated to match to some extent.

Anyway, I wanted to know more about the reticle, and there is a lot of contradictory info out there. I thought I'd measure for myself.

I took a yardstick and wrapped electrical tape every inch to increase contrast. Every five inches had different color tape, to make counting easier.

I placed this stick at 100yds, measured by the laser rangefinder. Here are my results fir the inches subtended by each BDC mark from the 100m mark. Numbers are to the nearest .25"

4x32 NSNTA01

100m 0"
200m 1.75"
300m 4.75"
400m 8.5"
500m 13.25"
600m 19.75"

3x32 TA33R8 - .223

100m 0"
200m 1.75"
300m 4.25" - Difficult to measure, since it's just the end of a line
400m 8.25"
500m 13.5"
600m 19.75"

One inverse tangent later, we obtain the drop angles (in minutes) from 100m, to the nearest .25'

4x32 NSNTA01

100m 0"
200m 1.5'
300m 4.5'
400m 8.0'
500m 12.75'
600m 18.75'


3x32 TA33R8 - .223

100m 0"
200m 1.5'
300m 4.0'
400m 8.0'
500m 13.0'
600m 18.75'
I used a 3x magnifier behind the ACOGs, which made things a lot easier. Of course this will magnify the image and the reticle equally, if there is no parallax. Acog parallax at 100m is pretty minor.

On the 4x I tried the measurements without the 3x magnifier. I could only get the 600m measurement, and it came out 20" +- .5 So the 3x magnifier doesn't seem to be an issue.

[a0cake]

Your measurements are highly accurate. Of course you could have just asked what the subtensions were and saved yourself the time, but I'm sure it was an enjoyable exercise anyway.

Now all you've got to do is figure out what ranges the BDC lines actually correspond to with your particular load and memorize them.

[ICANHITHIMMAN]

Your measurements are highly accurate. Of course you could have just asked what the subtensions were and saved yourself the time, but I'm sure it was an enjoyable exercise anyway.

Now all you've got to do is figure out what ranges the BDC lines actually correspond to with your particular load and memorize them.

So what are the actual numbers? I tried to get them out of Trijicon for years.

[QuietShootr]

Your measurements are highly accurate. Of course you could have just asked what the subtensions were and saved yourself the time, but I'm sure it was an enjoyable exercise anyway.

Now all you've got to do is figure out what ranges the BDC lines actually correspond to with your particular load and memorize them.

Yeah, but Trijicon won't give you that information. I was contemplating doing something like this with mine.

[a0cake]

Here are the numbers that I have written down. I got them from a handout that's been going around my old unit for years. I'm not 100% positive they're from Trijicon but they had to come from somewhere, and I don't think somebody in my unit went out and figured this out. They also closely match but are not exactly what "Shooter" produces for M855 @ 2900 FPS @ .304 BC in Army Standard Atmospheric Conditions. So, I have no reason to doubt the numbers. If they're not exactly correct, they're GD close. And if I had to guess, they come from Trijicon. If I had known this was in such demand I would have posted it earlier.

100M - 0 MOA
200M - 1.7 MOA
300M - 4.6 MOA
400M - 8.4 MOA
500M - 13.4 MOA
600M - 19.5 MOA

I've seen these numbers quoted elsewhere as coming directly from Trijicon for the 14.5'' guns, but I doubt them as they don't seem right. But it is possible that they are real numbers for another configuration and someone got it confused:

100 meters – 0 MOA
200 meters – 1.4 MOA
300 meters – 4.0 MOA
400 meters – 7.4 MOA
500 meters – 11.6 MOA
600 meters – 16.8 MOA

[StainlessSlide]

Now that I have the method down, I'll augment the post with any more ACOG reticles I get my hands on.

I have seen an ACOG-released table of angles for the 31F recticle on another forum, but can't find it now. I do remember that the 600m angle was 17-something minutes, a bit flatter than my NSNTA01.

Of course this supports the idea the NSNTA01 was intended for the issue load from a 14.5", the RCO-A4 is for a 20", and the 31F in between.

I look forward to measuring the others.

Added: I like your first table, a0cake. The second one looks more like the one I mentioned above.

[ICANHITHIMMAN]

just entered that data 2900 fps BC of 304 in my hand held got +4.1 mill or 14.0 MOA to a 600m target. I will try it again tomarrow when I have time to measure an SS109 bullet for exact specs.

[a0cake]

just entered that data 2900 fps BC of 304 in my hand held got +4.1 mill or 14.0 MOA to a 600m target. I will try it again tomarrow when I have time to measure an SS109 bullet for exact specs.

That would be ballpark for a 25M or a 300M zero but not for the ACOG's 100M zero. Honestly the first table I gave (or the OP's...they're very close) is 99% guaranteed to be the TA01 NSN's exact subtensions, or if not, so close that the difference doesn't matter.

[QuietShootr]

Placeholder for the TA11H-308 data (the M240 reticle) when I develop it.

It also has horizontal graduations for moving target leads.

I just had an idea that might make this a little easier. I know that the center dot of the horseshoe is 2 MOA. So what if I take a large piece of white paper, print a 2 MOA aiming dot near the top, and put it at 100 meters (laser measured). Then, I sandbag the gun with the dots superimposed, and get on a radio and have a friend with a Sharpie go downrange and mark the graduations PRECISELY on the paper, then just measure them. What say the group?

[StainlessSlide]

Placeholder for the TA11H-308 data (the M240 reticle) when I develop it.

It also has horizontal graduations for moving target leads.

I just had an idea that might make this a little easier. I know that the center dot of the horseshoe is 2 MOA. So what if I take a large piece of white paper, print a 2 MOA aiming dot near the top, and put it at 100 meters (laser measured). Then, I sandbag the gun with the dots superimposed, and get on a radio and have a friend with a Sharpie go downrange and mark the graduations PRECISELY on the paper, then just measure them. What say the group?

This method sounds great.

If a database of lots of different ACOGs is developed, obviously it will be easier to find a reticle that is close to one's favorite off-caliber or off-milspec load. I'm curious about the 6.8 reticle.