I have a 4x ACOG that is made to be used with a 14.5 barrel. I actually have a 16" barrel. How big of a deal is that?
Its fine. True your zero at whatever range you can shoot.
Depends on your ammo. Using different ammo is a bigger problem than barrel length. Shooting very similar ammo, zeroing with that ammo, and knowing your points of impact will help.
what change, if any would I notice?
I shoot 55gr federal xm193
Lets establish your requirements. How far are you trying to shoot, and at what size target?
my range goes out to 600. They have targets from grapefruit size to man size.
Independent of optic and barrel, you’re gonna hate XM193 at that distance. If you true the Z at 4, 5, or 6, and then experiment a bit, the ACOG won’t be your limiting factor.
I zero at 100 yards right on the dot of the reticle. I’ll just give it a go I guess.
Sweet. Let us know how you fare.
Edit: I just checked my chrono data, and Fed XM193 was much better than Winchester, FWIW.
Depending on your barrel, ammo changed can change your POI enough to be annoying. Windage shifts are the most irritating.
The reticle will track pretty good if your zeroed at 100.
Don’t overthink it. The BDC is not a precision instrument. The intent of it is for a “close enough” holdover for a quick shot (or 4-5 shots). If you want precision, then go to something with an MOA or MRAD marking so you can run the calculations youruself with specific loads.
Exactly.
elevation, temperature, air density, moisture, load, even the smoothness of the barrel are likely to be as much, or more, of an issue.
i’ve rarely had an acog match a particular AR in the last 30 years of owning them, and i’ve had a bunch.
even if its off a bit, no big deal. we’re talking “minute of target” here, not precision bench rest.
besides, there are a number of ways to adapt using each scope to each rifle. shoot it to find what works for you.
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The “C” in ACOG is for “Combat.”
It was designed to kill E-type silhouettes 40 inches (one Meter) high by 19.5 inches (half a Meter) wide – not itty-bitty plates and X-rings (although they can, with the proper ammo, trigger, and shooter).
I recenty got the chance to measure the accuracy of the BDC on steel out to 600 with a 6920, 55gr, and TA31 RCO. Out to 300, hits were right on. 400 and out the BDC was WAY off. Better ammo would likely result in a truer BDC.
For issued GI 14.5 barrels and 16-inch commercial barrels I’ve found by experience (coaching military and ROTC Cadet combat shooting teams) the best general-purpose combination has been the TA01B (308/7.62 reticle) with GI M855A1 or commercial 69-77 grain bullets.
The reticle generally holds true to 400/500, though group dispersion due to any side winds opens up.
It is what it is. Disabler of a threat. Not a swiss time piece. With that said, the optic is cut to a particular set including length of barrel and one type of “mil-spec” box ammunition.
Like anything, you must compensate when drifting from those specs. Easy enough but when doing that, your goal should be consistency. Make notes, memorize, march on.
I shoot 2 ACOGS on SBR’s and using a the “programming for drop” that is fixed match a bullet and velocity as c
Ose as possible to the ballistic curve given. This works wonderfully