Hi All,
I’ll be picking up a KAC SR-15 next week and running a TA31H on it. I believe (correct me if I’m wrong) the TA31H is designed for .62 grain Ammo. Should I zero it At 100m with .62 grain or should I use something like a .75 or .77 grain match ammo? Now hear’s the other twist, If I’m going to be using .55 grain for practice, How much of a issue will this be???
Thanks for the help!
They are designed to work with 62gr (not .62gr ;)) ammo from a 16" barrel at moderate velocity.
ETA- This information is incorrect. I don’t know what I was thinking. The correct info is below in JSantoro’s post.
Apologies.
Really though, the most effecive way to get a solid zero is to confirm and adjust at 300 meters, regardless of what ammo you are using. It might make you slightly off at 100, but your 300 will be dead-on, and your 4,5, and 6 will be much closer than if you only zeroed at 100.
When switching ammo you can experience anything from slight to drastic changes in POI. Test to see how much your selected training ammo deviates from expected POI before heavily investing or you will have to re-zero every time you switch ammo if you want to get quality training. Don’t forget, just because you are close doen’t mean that you can be sloppy, and if you train to be precise with an incorrect hold you may wind up being imprecise with your duty ammo when the time comes.
Quick question on that: since the ACOG doesn’t have a 300 yard hash mark, how do you “confirm” at 300?
Rohardi, you’ll love the SR, I have one, and it’s the sweetest shooting AR I’ve ever fired. I went with tthe TA31RCO, but should have saved $200 and bought the H reticle, that thing looks sweet.
Very cool!
I decided to zero mine in using the grain I will be most likely stock piling for a shtf scenario, which for the most part is 55gr.
From the Trijicon FAQ page: http://www.trijicon.com/faq.cfm
- What bullet was used to calibrate the ACOG scopes?
The TA01, TA11, & TA31 (.223) were designed for the 5.56mm, 20 inch barrel, 55 grain bullet, and M16/AR15 carry handle mount. The TA01B & TA11C(.308) were designed for the 7.62mm, 20 inch barrel, 168 grain bullet, and M16/AR15 carry handle mount. The TA01NSN was designed specifically for the US Special Operations Command SOPMOD M4 Carbine. To meet their requirements, the reticle bullet drop compensator and range finding stadia lines were based on the trajectory of the 62 grain bullet from a 14.5 inch barrel, flattop mount (Picatinny rail Mil.Std.1913).
Now, perhaps a dozen or more type-specific ACOGs have come out since this was initially printed, and it hasn’t been changed. If the above doesn’t tell you what you need to know, you’re best served calling in to Trijicon and confirming what round your BDC is tuned for.
This is one of the biggest disconnects when it comes to ACOGs. They were designed with military use in mind, and there’s isn’t a single First World military in the world that fights in yards, as evidenced by the fact that military maps utilized by the ground combat element are all gridded out in meters. The BDC is in meters, which are not the same measure, and the difference gets greater with farther distances. 100m is 109yd, or 27’ of difference. Not much impact on the nearer side, but it pretty relevant in a hurry.
Blue-water Navy still uses yards on their charts, but they’re generally not plinking at each other’s hulls with carbines. Plus, screw those guys. 
It absolutely has a 300 meter aimpoint (top of the BDC, the tip of the vertical red line), so you go for 300m (328yd), or utilize the 300m mark at a 300yd target, and know that you will print high, by around 2-3", depending on ammo type. Something like .5" high @ 325yd.
Or, you use the 300m aimpoint @ 300yds, then shoot at other distances to see how far off on the reticle, as designed, you are.
I based the above on an SR-16 w/M855 @ 2900fps, with a sight height of 2.755" (TA31RCOM4, stock TA51 rail mount). How high for another gun/ammo combo can be determined by punching your ammo’s specifics into a ballistic calculator.
If I remember correctly, I called Trijicon before I bought my TA31F. My reason for purchasing the TA31 series is mainly because they told me it was the only model where the BDC was calibrated on a 16" carbine (which is what I have). Anyway, to answer your question, yes, they told me that they calibrated the TA31 series with a .62 grain.
I don’t think there is a difference between the .55, .62, or, .69 grain at 100 yards…well that also depends on the rifling ratio on your barrel (1:7, 1:9, 1:12).