Rifle Scopes Trijicon TA31H - question about application.....

[jkazak]

I'm a newbie here and also new to the world of tactical guns, so please forgive anything that seems ignorant.

I just purchased a new ACOG TA31H (for what I thought was a smoking deal) thinking I was going to put it on my STG-556. While the Trijicon was still en-route I came across more info on it that now has me wondering about my choice.

For starters I learned that Trijicon calibrates this unit for a 5.56 round with a 55-grain bullet out of a 20-inch barrel on top of an M16 carry handle. I am planning on shooting a 75gr bullet (also 5.56 pressure) out of the 16-inch barrel on a flat top rail of the STG-556. I'm not sure how the ballistics compare between the 2 different bullets, but I'm now wondering if this can be made to work - or did I make the wrong choice.

I think the ACOG is a well made scope (although the eye-relief is awfully short) and if I can get used to that and keeping both eyes open all the time, I thought it would make a good SHTF combination with the bull-pup design. But it won't do me any good if the scope won't work with the rifle....... especially if the BDC is useless.

Again - I'm new to all of this so if I seem un-educated it's because..... well, I am.

Next thing that has my peanut brain going is......

If a specific rifle likes a specific bullet at a specific pressure it seems to me that there should be a mathematical equation that will tell us a specific optic that would work best for that gun/round in a (mostly) specific application (i.e. distance). Which should tell how much usable distance we have and hence how much scope power is practical and how much more power is wasting our money. Is this practical or am I overloading my peanut ?

 

[CanPopper]

Re: Trijicon TA31H - question about application.....

First, the question is range. With a 16 in barrel gun, you probably aren't going out very far (200 yards and below) so the error on the BDC won't be significant (like around an inch or less at 200) while zero is zero'd.

The 75 gr bullet is about 200-300 fps slower than a 55 gr for the same barrel length. Then shooting it out of a relatively short barrel will decrease its velocity again. Why not shoot a 50-52gr bullet instead if the bdc lining up means that much to you?

 

[jkazak]

Re: Trijicon TA31H - question about application.....

Thanks for the reply. The reason for the heavier bullet is the heavier retained weight after impact. Also the round I intend to use (Hornady TAP) seems to have as good a reputation as the Black Hills 77gr that is so highly regarded for a tactical defense round - and can actually be found !

You make a very good point about the BDC actually lining up - with the right amount of practice the BDC should really be used as a guideline and actual shot placement should be a matter of experience - true ?

 

[CanPopper]

Re: Trijicon TA31H - question about application.....

Yup. I have a Burris scope with BDC.

The way I know where my bullets are going to hit for each hash mark is I chrony the bullet and enter its info into an online ballistic calculator. From that result, I know whether the bullet is going to hit above or below each of the hash marks for each range and by approximately how much.

For your rifle, it will be a bit below for the 200 hash mark with a 100 zero. But unless you are trying to shoot clover leafs with your gun, such an approximation will be enough.

In urban combat (and especially home protection), its not like you are going to be defending it with 300 yard shots. Most likely, the engagement will be under 100 yards.

 

[Redmanss]

Re: Trijicon TA31H - question about application.....

Found the below info for the TA-11H stadia lines searching around on the web with the claim he got it from Trijicon. From what I came up with, you only have a 1moa difference at 500m, 13.9 drop from 100m zero with the data for the TAP I swagged.

There's a lot smarter guys than I am with the ballistics tables on this forum, so maybe one of them will chime in with some more accurate data.

<span style="font-style: italic">dots = 2 MOA
horseshoe = 11 MOA
windage dots/hash marks = 5 mils

center dot = 100 meters zero
400 meters = 8.3 MOA
500 meters = 13.1 MOA
600 meters = 19.2 MOA
700 meters = 27.1 MOA
800 meters = 37.2 MOA</span>

Source Posting

IMHO, I really wouldn't sweat the little stuff. Mount your ACOG, shoot your choice of ammo that performs well out of your rifle, and have a great time with it. With a 4x scope and a 16" barrel, you aren't going to be splitting hairs anyhow. Have fun with the controlled pairs instead.

 

[problemchild]

Re: Trijicon TA31H - question about application.....

As far as short eye relief goes the TA11 series have about 3.5" of eye relief.

 

[jkazak]

Re: Trijicon TA31H - question about application.....

Just found this - more than my brain can handle all at once.... Wow. Good Info.

http://demigodllc.com/articles/practical-long-range-rifle-shooting-equipment/

 

[JTinIN]

Re: Trijicon TA31H - question about application.....

One option is to shoot the scope, rifle and ammo at distances from 100 to 600 yards and note where each line hits.

Thus you might end up with 400 being a 440 yard line ... not too bad until you have three ACOGs ;-).

 

[Zhurh]

Re: Trijicon TA31H - question about application.....

I put a 4X32 red ghost ring Acog set up for 6.8 on my Stag. I really like it for those right after dark shots.

I had an Indian neighbor who had moose forever bothering their horses. Now some horses don't mind the moose but Stella's horses went nuts; so she would just shoot the moose with an old 243. I saw her shoot over 20 moose over 7-8 years and none walked off. So I bought that 6.8 spc and acog for after dark shots when moose often come out.

I've thrown that red ghost ring up on several cows just to see it in action. Works fine rght after dark and no batteries, but not as bright as during daytime. Haven't tried the B&C lines out, but holds inch circle at 100 yards. I really like it on 4 wheeler with team sling; quick to pull up and get on target riding down a trail or road.