Which ACOG to get?

[a1madrid]

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.

The TA31RCO looks like a very good option. I looked it up and Trijicon advertises it as BDC for the M4 (14.5 inch barrel). This should match up pretty close to what I plan on building. Now I was planning on running a Silencerco 5.56 Saker K on the end of my 12.5 build. Even with it being a K can and not a full length 5.56 can, do you still think the velocity will be close enough to an unsuppressed 14.5? I know I’m splitting hairs here but this is good information you just gave me thank you.


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[1168]

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.

Absolutely. There’s some weird barrel voodoo that can whack your bullets a couple minutes off, whereas some don’t seem to care at all. I think as long as he zeros it with whatever case he’s shooting at the time, the ACOG will do its job, though.

[a1madrid]

Absolutely. There’s some weird barrel voodoo that can whack your bullets a couple minutes off, whereas some don’t seem to care at all. I think as long as he zeros it with whatever case he’s shooting at the time, the ACOG will do its job, though.

That’s what I plan on doing.


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[1168]

The TA31RCO looks like a very good option. I looked it up and Trijicon advertises it as BDC for the M4 (14.5 inch barrel). This should match up pretty close to what I plan on building. Now I was planning on running a Silencerco 5.56 Saker K on the end of my 12.5 build. Even with it being a K can and not a full length 5.56 can, do you still think the velocity will be close enough to an unsuppressed 14.5? I know I’m splitting hairs here but this is good information you just gave me thank you.


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If you buy 10 12.5” barrels and put cans on them, and 10 14.5” unsuppressed barrels, you may see overlap in velocities, especially if the 14.5” guns have a bunch of rounds through them (.mil). In any case, the difference will almost certainly be unnoticeable.

And, you’re welcome.

[a1madrid]

If you buy 10 12.5” barrels and put cans on them, and 10 14.5” unsuppressed barrels, you may see overlap in velocities, especially if the 14.5” guns have a bunch of rounds through them (.mil). In any case, the difference will almost certainly be unnoticeable.

And, you’re welcome.

Even with running a shorter can like a Saker K from SilencerCo?


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[1168]

Even with running a shorter can like a Saker K from SilencerCo?


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Yeah, absolutely. The velocity difference, unscientifically between a 12.5” and a 14.5” is roughly 100fps, making a 12.5” pretty much halfway between an 11.5” and a 14.5”. But I’ve observed freebore boost as high as 75fps with K silencers. Its typically a little less, 25-40fps, sometimes none.

So, we can say that in many cases a 12.5” is somewhere within 100fps or less of a 14.5”, which isn’t really that much more than the extreme spread with ball ammo. Peep my chrono thread here: https://www.m4carbine.net/showthread...5-56-data-1168 and this dudes chrono thread over there: https://www.ar15.com/forums/ar-15/-/16-714088/? Note that with one brand of ball ammo, he showed only 10fps difference between his 12.5” and 14.5”.

The variability from one barrel to the next can easily be 100fps, so its really not that much difference to the reticle. Add in varying temperatures throughout the year, and you’ll see that the ACOG’s reticle has to accommodate a spread in 14.5” velocities that would overlap with a 12.5” or a 20”. Also, with the reticle made for 62gr from a 14.5”, and you shooting 55gr from a 12.5”, it’ll probably line up pretty close within about 500~ish yards. After that, BC and errors in range estimation start to matter more than 100fps.

I’ve got a 14.5” thats getting old and slowing down, about 50-75fps slow, and there is overlap with my newest 12.5” using 62gr and 68gr ammo. Sometimes the 12.5” is actually faster, and that was also true of my last new 12.3” barrel and its 1 year older 16” friend that was slow.

I forgot to mention… there’s another choice to make with ACOGs: do you want short eye relief with a great field of view and 4x, or do you want longer eye relief with less field of view and 3.5x?

[markm]

I always thought that free bore boost was a bunch of liberal propaganda. I've never measured it. People used to also say that suppressors slowed the bullet down too.

[Slater]

Which (if any) ACOGs were designed to be compatible with a rifle-length weapon?

[1168]

Which (if any) ACOGs were designed to be compatible with a rifle-length weapon?

I think the TA31RCO was issued in the corpse with A4s. Someone will have to check my memory.

[a1madrid]

Yeah, absolutely. The velocity difference, unscientifically between a 12.5” and a 14.5” is roughly 100fps, making a 12.5” pretty much halfway between an 11.5” and a 14.5”. But I’ve observed freebore boost as high as 75fps with K silencers. Its typically a little less, 25-40fps, sometimes none.

So, we can say that in many cases a 12.5” is somewhere within 100fps or less of a 14.5”, which isn’t really that much more than the extreme spread with ball ammo. Peep my chrono thread here: https://www.m4carbine.net/showthread...5-56-data-1168 and this dudes chrono thread over there: https://www.ar15.com/forums/ar-15/-/16-714088/? Note that with one brand of ball ammo, he showed only 10fps difference between his 12.5” and 14.5”.

The variability from one barrel to the next can easily be 100fps, so its really not that much difference to the reticle. Add in varying temperatures throughout the year, and you’ll see that the ACOG’s reticle has to accommodate a spread in 14.5” velocities that would overlap with a 12.5” or a 20”. Also, with the reticle made for 62gr from a 14.5”, and you shooting 55gr from a 12.5”, it’ll probably line up pretty close within about 500~ish yards. After that, BC and errors in range estimation start to matter more than 100fps.

I’ve got a 14.5” thats getting old and slowing down, about 50-75fps slow, and there is overlap with my newest 12.5” using 62gr and 68gr ammo. Sometimes the 12.5” is actually faster, and that was also true of my last new 12.3” barrel and its 1 year older 16” friend that was slow.

I forgot to mention… there’s another choice to make with ACOGs: do you want short eye relief with a great field of view and 4x, or do you want longer eye relief with less field of view and 3.5x?

In the second thread you linked me to, he was shooting a 12.5 suppressed and the 14.5 was suppressed as well. So theoretically as close as those numbers are on that chart between the two barrel lengths both suppressed, they should be even CLOSER for a suppressed 12.5 compared to an UNsuppressed 14.5 since the suppressed 14.5 is probably getting some additional velocity boost off of that can, correct?


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