Which ACOG to get?

[a1madrid]

So my next AR is gonna be a 12.5 inch barreled gun with a carbine length gas system. I’m pretty set on running an ACOG on it. If you go on Trijicon’s website there are tons of 4x options that claim to have the BDC for 5.56. I know that the model the military has used extensively on the M4 is specifically calibrated for the BDC out of a 14.5 inch barrel. Now looking at the ballistics out of a 12.5 inch barrel vs 14.5 inch barrel, there is some loss in velocity but it is not a HUGE loss. I have seen a decent amount of people running ACOGs on 12.5 setups but my question is which 4x option will matchup CLOSEST to 12.5 ballistics? I saw on a livestream Lucas from TREX arms was running an ACOG on a 12.5 and he said he was hitting steel at 400 easy with it, which is all I would expect the 12.5 to do. I’m assuming the model that will match up CLOSEST to the ballistics of the 12.5 is whichever model is calibrated for the bullet drop of a 5.56 out of a 14.5 barrel but I want to know which one specifically? And do they make that model with a green chevron or with any green options? I also was planning on running this gun suppressed full time so I’m assuming I will get some velocity back but not a whole lot. And the majority of the stuff I will be shooting and what my guns are zeroed with is 55 grain XM193. Thanks guys.


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[1168]

NSN version for 62gr should be pretty close, if you true it a little further out.

[a1madrid]

NSN version for 62gr should be pretty close, if you true it a little further out.

Also, the majority of the stuff I will be shooting is 55 grain XM193.


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[markm]

I just set up my 14.5 with a TA01NSN, and I'm running 69 gr RMR bullets hand loaded to about 2850 fps.

I was sure the load wouldn't keep up with the reticle, but the ammo is actually outpacing the reticle. I'm holding belt buckle on a 500 yard target to get close to center mass.

My COG and load would likely match up good with a 12.5. I bet XM193 tracks pretty good.

[bamashooter]

As you know, ACOG and all others are spec'd to a single round and whether people want to admit it or not, a specific barrel length. Just they way it is and can only be. With that said, extended distances aside and a willingness to accept a less than designed for result, you should be able to satisfy your desire for an optic with BDC; within reason. You should be able to get a disabling hit at under 400m / multiple quick hits <300m once you establish your primary zero.

[a1madrid]

As you know, ACOG and all others are spec'd to a single round and whether people want to admit it or not, a specific barrel length. Just they way it is and can only be. With that said, extended distances aside and a willingness to accept a less than designed for result, you should be able to satisfy your desire for an optic with BDC; within reason. You should be able to get a disabling hit at under 400m / multiple quick hits <300m once you establish your primary zero.

I’ve seen videos of people hitting steel out to even 500 yards with them on a 12.5. If it was still a combat effective reticle on a 12.5 out to 400 yards I would call that a success. But again I am not sure which 4x ACOG to go with. Whichever model is for the 14.5 I would assume would work best but I don’t know.


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[1168]

Also, the majority of the stuff I will be shooting is 55 grain XM193.


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If your main objective is just getting to 400, I think you’ll be fine with a version meant for 14.5” M855. XM193 from a 12.5” barrel isn’t too far off in velocity from M855 from a 14.5” gun, so it should work. Like MarkM, I shoot 68gr ammo to 500 or 600 using BDC reticles similar to the ACOG’s all the time. None of those reticles were designed for that ammo weight, and most weren’t even designed around my 14.5” or 12.5” barrels, but I do just fine.

Are you using Winchester, or Federal XM193? What target types?

[a1madrid]

If your main objective is just getting to 400, I think you’ll be fine with a version meant for 14.5” M855. XM193 from a 12.5” barrel isn’t too far off in velocity from M855 from a 14.5” gun, so it should work. Like MarkM, I shoot 68gr ammo to 500 or 600 using BDC reticles similar to the ACOG’s all the time. None of those reticles were designed for that ammo weight, and most weren’t even designed around my 14.5” or 12.5” barrels, but I do just fine.

Are you using Winchester, or Federal XM193? What target types?

The mix of my ammo stash right now is Hornady Frontier XM193, Federal American Eagle XM193, and I do have some of PMC’s XM855 load too. The majority of what I shoot and what I will buy in the future is XM193. Keep in mind I am also going to be running this gun suppressed a lot of the time too. So that will bring SOME (not a a lot but some) velocity back as well, narrowing the gap between 12.5 and 14.5 ballistics a little bit more.


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[1168]

The mix of my ammo stash right now is Hornady Frontier XM193, Federal American Eagle XM193, and I do have some of PMC’s XM855 load too. The majority of what I shoot and what I will buy in the future is XM193. Keep in mind I am also going to be running this gun suppressed a lot of the time too. So that will bring SOME (not a a lot but some) velocity back as well, narrowing the gap between 12.5 and 14.5 ballistics a little bit more.


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On E-types, you could probably mix all of those up in a mag and hit at 400 with a 12.5” and ACOG. With B/C steel or F-Types you’ll likely be fine with whichever you zero it for. They’ll all be moving close to the 2950-3150fps the reticle is designed for.

I think you’ll be fine with a TA31RCO or a TA01NSN, in that order.

Edit: *the difference between a 14.5” and a suppressed 12.5” velocity is rather slim*

The key to using different ammo and barrel lengths than what a reticle is designed for is to true it up further out. If your zero is perfect at 100, it might be significantly off at 500 with the hold marks, if the velocity is too far off. But if you true it up at 400-500, it’ll be good enough from 0-500.

As an example, I’ve been shooting an 8x LPVO with a reticle designed for 20” barrels, but I’m using on a 14.5” thats old enough that the velocities are slightly under that of my 12.5”. I zeroed it at 300, then shot 500 and made a couple small adjustments. Both with 68gr Frontier 5.56. I then shot third in a match that went out to 500. And now I’ve discovered I can put 55gr steel case in it and hit to at least 400 with ease, without touching my zero.

Sidenote, I’d stop buying that Frontier ammo. I’ve gone through 3 cases of the 68gr 5.56, chronoing 5-10% of the case. Each case has had one round thats around 200fps faster than all of its friends in the same 12.5” or 14.5” barrels. That means that there is probably around 10 overpressure events per case in the 90+% that don’t get seen on a chrono.

I think the 193 clone Frontier is the one associated with kabooms on TOS.

[markm]

He should also check his POI with all the ammo types at 100 yards. Barrels are sometimes weird where they'll shoot way off with different projectiles.