Trijicon TA31F ACOG

[JGarcia]

We've been doing some figuring and studying on the TA31F ACOG here at the school. Supposedly the reticle is for an M4 firing M855 ammunition, but the numbers don't exactly add up.

Out of curiousity does anyone know if Trijicon uses a 6400 miliradian circle or the mathematically correct 6283.2 miliradian circle?

I've been doing some figuring on my own tonight and the red chevron which is supposed to equal an E Type at 300 M doesnt quite add up, using either 6400 Mils or 6283.2 Mils, but 6400 is about 5 Meters closer than the mathematically correct 6283.2.

I worked it out like so,,,,

19.5" wide E type X 25.4= my constant of 495.3 divided that by the mils I got from converting their MOA data for that reticle from MOA to mils, using both 6400 and 6283.2.

Using 6400 mils I get 304 M.
Using 6293.2 mils I get 309.6 M.

The width of bottom of the red chevron, should equal 19.5" or 300 M.

So, let me go back and see if I can find any errors, in my assumptions. Maybe they used a number other than 19.5" wide for the E type.

It also looks like the figured the BDC with a 20" barrel, even though the reticle is supposedly for an M4. Wont make a difference for most, but just thought you might like to know; zero accordingly.

[JGarcia]

Yep, the bullet drop on the TA31F reticle is definitely for 20" barrel firing M855 ammo; it is NOT correct when it comes to bullet drop for an M4, never mind that it is supposed to be for an M4.

[dmgedgoods]

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[desertmedic]

J,

The manual for my RCO-M4 states 19" for the base of the triangle and BDC hash marks at their corresponding ranges. Can't find anything on the mil math they use on the ACOG. Sent you a PM. Stay safe,

Desertmedic

[The Reaper]

Originally Posted by JGarcia

Yep, the bullet drop on the TA31F reticle is definitely for 20" barrel firing M855 ammo; it is NOT correct when it comes to bullet drop for an M4, never mind that it is supposed to be for an M4.

The answer from Trijicon is:

1: The width of the TA31F chevron represents 19 inches at 300m. Not 19.5 inches. Also, one may need to reduce a possible “ballooning” effect of the chevron if it is under bright light. This may make the chevron appear larger than it is. The tried and true solution for this is placing some riggers tape over the fiber optic tube to adjust brightness.

2: The BDC of the TA31F is not based on the trajectory of a 14.4 inch or a 20 inch barrel- it is based on 62 grain bullet exiting a muzzle at 3050 ft/sec (about a 16 inch barrel).

3: The TA31RCO-M4 (USMC RCO, carbine version) and the RCO-M150 (US Army RCO) both have their BDCs based on the trajectory of a 62 gr bullet from a 14.5 inch barrel.

Hope this answers the mail.

TR

[dmgedgoods]

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[Gene Econ]

Originally Posted by dmgedgoods

From what I gather on the info I have for our ACOG's, it is 19", not 19.5". Can you explain the math you did for us less literate in ballistics? This is good info for me to use when zeroing and training our guys up on these pieces of equipment. Shawn

Shawn:

Take fifty issued M-4 Carbines, 50 issued ACOGs that actually work, M-855 ball and fifty Soldiers just trained for five days by an MTT from the AMU and who consider themselves to be 'Designated Marksmen' because they have a piece of paper stating such.

Tell me if you think that a barrel length difference of 1/2 inch will make an iota of difference with a 3 minute carbine, a 2 minute optic, 4 minute ammo, and a 10 minute shooter (who was probably a five minute shooter before the AMU got to them).

I think some of you guys could be considered delusional or perhaps clinically insane.

[dmgedgoods]

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[Gene Econ]

Originally Posted by dmgedgoods

Just mostly interested in the math of it all. I have never had to concern myself with the math before, and don't plan on becoming an expert online, but it is still interesting. Shawn

Shawn:

Roger -- my response was irresponsible. Not enough humor.

TR gave the poop. Not sure what JG was asking and won't open a can of worms.

I figure you can use the optic in question on either to the effective range of a service grade rifle firing service grade ammunition -- about 500 yards. Remember that there are variances in precision of reticle manufacture and those ACOGs are pretty low power with pretty thick cross hairs. Obviously, you want one that matches as closely as possible your rifle and ammo but to me with carbines, A-2's, or A-4's -- the average trained rifleman and service ball ammo things get so problematic that I just view all of them as pretty much the same.

Gene

[RichL025]

More sarcasm sir....

I still need to come by and check out your boomstick collection one of these days Gene... Damned if I know why but I keep getting crazy thoughts in my head about building a service rifle....

Rich

[Gene Econ]

Originally Posted by RichL025

More sarcasm sir....

I still need to come by and check out your boomstick collection one of these days Gene... Damned if I know why but I keep getting crazy thoughts in my head about building a service rifle....Rich

Rich:

Roger that -- let me get my new floor down and the interior painted (about three more days) and you are on. You missed a decent day today. 50 and sunny. The guys did real well but we were a ways away from MAMC so I doubt you heard us blasting.

Gene

[JGarcia]

Gene,

Our resident old fart (Presidents Hundred) is always drilling me on odd ball stuff which usually has me (and everyone else) stuttering and stammering with his questions.

This ACOG thing was one of them. It started because he wanted me to figure out how to get the MILS for the TA31F reticle given some data he provided me with.

I did it.

We finished our SDM course out at Camp Roberts, CA last week. We had a great time, graduated 27 students after two weeks of training. They came to training with the M4 and TA31F. The wind and light conditions were near ideal on test day, consequently we had some pretty high scores. The weather was mostly overcast and light sprinkles the rest of the time. We had one broken ACOG that somehow the prism cracked and got fogged over inside. This occurred on the 600 yard and in KD range test day, the shooter had to use his partners weapon and dope book, he passed.

The KD and UKD ranges at Camp Roberts, CA are excellent. On the KD range we could have trained 48 students if we had enough instructors. UKD range goes out to 1000 or more; the firing line is very wide about 170 yards, no significant dead space and no prominent fixed objects to assist in range estimation which made it a little more difficult than the range estimation exercise at Camp Robinson, AR. The unit we trained provided a dedicated range detail that did a ton of work for us which allowed more training time for students.

Camp Roberts, CA range control has no iron maidens, if you go out there to teach you will need to bring your own. They also had no spray adhesive for targets on the 6'x6's but they did have the paste you have to mix up. Classroom facilities are decent, but small. Range control was easy to work with and on the ball.

The guys shot very well out to the 600 Meter range, we nearly had a three way tie for top gun and had to have a shoot off. Good times. We typically set up a 700 Meter target and this time was no exception, we ranged it at 757 Meters, a few of our best students were capable of hitting it several times, but as I said conditions were ideal. We did notice some anomalies with the M4 back up iron sight that indicated either a couple of Soldiers reverting back to bad habits after three days of shooting or a 4 to 5 MOA windage error when changing from the 400 to 300 setting / yard line. Not quite sure about it yet so we are going to try and get our hands on some of these sights and experiment. We hope to be out there again this summer for another MTT.

One last thing. There was a very large squirrel population on the UKD range, and that's all I am going to say about that.