ACOG TA31F-G Assistance Please

Tactical Gear Optics & Mounts
1

Greetings all.

Didn’t see an intro section. I’m not much of a Forums Poster. I’m of the mindset that 99% of what you are looking for can be found by simply searching. Well, I have hit that 1% apparently.

It seems custom to provide a quick “hello” on a lot of forums so I will just say I am your typical middle age family man with kids and a wife and live a pretty normal life living in North Texas. (Hook 'Em) I don’t do any hunting I just own a few firearms for self defense and anything else that might pop up. (SHTF etc.) Been a long time lurker of this site and others, but as you can tell this will be my first post.

First my specs. I have a Bushmaster 15 Optic Ready with a 16in Barrel and a 1/9 Twist. It has a Wylde chamber that fires both 223/556 and has a flattop mounting surface. I mainly shoot 55gr bullets (I have multiple in stock) with a few 62gr green tipped (like 300 rounds) that was given to me. Other than that, ALL my defense and SHTF ammo is in 55gr. (Just prefer 55gr as my wife has an AR too and she shoots it well. Makes cost easier) My wife and I have only fired out to 100 yards so far. (no range in meters around my area that I can find and so far I haven’t had the need to extend that range)

I got a tremendous deal (500 beans) on a lightly used TA31F-G Scope. Here are the questions.

I’ve read about the scope being “calibrated” for a 62gr bullet. I also read that one thread in the FAQ about the BDC. What I didn’t see in any of the FAQs or threads is: what grain bullet do I USE to zero it? Do I HAVE to use 62gr to zero it with since it’s calibrated for that? What if I use 55gr? is the BDC now off? The manual didn’t say and Tech support gave me a few “uhhh” and “maybes”. Or, am I being a schmuck and splitting hairs? If I use a 55gr to zero it, just how far off will the BDC be? Does it even matter? Worst case scenario, I MIGHT see myself shooting out to 300 yards / meters. IF that happens though, the world has gone to hell in a hand basket.

Also, am I FUBAR if I don’t use 100 meters? I only have access to 100 yard ranges. I hate to sound like a worry wart but I am what you call one of those nimwits that like to have everything in working order. (You should see me clean my guns)

Well that is about it. Sorry if these are remedial questions but to be honest I really hate going half way with stuff. I’d like them to be as perfect as I can get them. For the record, I have shot it mounted and it is off by a hair or two, meaning not quite center mass. I have shot both 55gr and bought a cheap box of 62gr to see and they both were off so I didn’t want to start fiddling with it until I figured out the above info.

You guys have been a fountain of info for me so I appreciate the education I have gotten the past year or so reading these forums. Thanks for any assistance that is given. By the way, if someone tells me to read the FAQ please provide a link to the possible thread that I missed. It would be helpful and appreciated.

Thanks again.

Kevin AKA “Lud”

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I have the same set up as you. First I sighted in at 100Y useing 55g. Remember your only 9Y’s short for a 100m. I have checked the BDC out to 300Y not over 1/2" difference. The TA31 isn’t a tack driving sight it’s for MOM. I have used this set up on hogs and deer and am happy with results.

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Thank you sir. That’s what I was hoping to hear. I really didn’t want to go out and restock in 62gr and get rid off all my good stuff in 55gr. Salute to you sir

4

The ACOG is not meant as a precision optic by any means. There will be deviation from the BDC calibrated for 62gr M855 and your regular 55gr load. But, so long as you zero it at the 100 meter mark as designed, the amount of deviation you see in the BDC from load to load will be within a typical shooter’s “wobble zone” out to a few hundred meters and probably won’t even be noticeable.

A lot of guys shooting 77gr SMK loads note that the BDC on the 7.62 reticles is a closer match than the 5.56 reticle. In any case, if you want to do serious shooting with it, it won’t be too difficult to figure out your exact drops for each range.

5

Thank you for your reply BrigandTwoFour.

Yeah I hear ya on the ACOG. We already had one “AR” (I hate using that acronym)15 at the house and put a precision scope on it for plinking and for shooting and just to have some fun with my daughters. We decided to build another for “Defense” so to speak, hence the ACOG purchase. I am just one of those dudes that could never live with the phrase “It’s good enough.”
if I have something, I want it to work as flawless as possible. I also didn’t want to purchase a whole bunch of new ammo.

On two lighter notes. 1. I got my Tax Stamp back today on my Suppressor build. WEEEEE! Now time to research that and 2. more directly related to this thread, Trijicon responded to an email that I send about two weeks ago. Here is their reply to my questions for help purposes if anyone does a “search” looking for the same information I was:

Good Afternoon

Thank you for your patronage of Trijicon products. See answers following each question, and contact us if you need further assistance.

Regards

Greetings. I purchased an ACOG TA31F-G and had a couple questions.

I was reading through the manual and may have missed this information, and Google seems to not be providing the information I was needing. Is there a specific round I am supposed to use to zero my scope? THEIR ANSWER: (They said red but you probably won’t see that) – Most flat-top models calibrated based on 62 gr projectile

I keep reading it was designed for a 62gr bullet, but I was intending to shoot 55gr bullets. Will the BDC not work for 55gr or can I zero with a 55gr and be on target with both 55 and 62 gr? THEIR ANSWER: (They said red but you probably won’t see that )-- There will be a small deviation using a different bullet weight, but even an above average shooter may not fully realize.

I can’t find a range that is 100M. Can I use the 100 yard range? THEIR ANSWER: (They said red but you probably won’t see that) – Again, designed for 100 meter ZERO. Difference will increase with distance.

Someone told me my scope was designed for a 20" barrel. Mine has a 16" barrel. Will I need to mount this thing any different to make it accurate? THEIR ANSWER: (They said red but you probably won’t see that) – No, this model based on bullet weight and velocity. Ideal for your platform.

I apologize for the remedial questions. I appreciate all the assistance you can give me. Thank you for your time.

Eric Lockhart

Customer Service Representative

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I think they were a little simple on their answer. The BDC in the TA31F is calculated for a particular ballistic coefficient of M855 (.304). Velocity is a factor of powder load and barrel length, so for a standard cartridge (M855), the only real way to increase velocity is a longer barrel.

That said, I believe the TA31F BDC is an average of the 20" velocity and a 14.5", meaning your 16" should be just about right on.