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Discussion Starter · #1 ·
I was looking at some ACOGs the other day (I'm not exactly looking to buy one, too expensive) and I noticed that there were some configured for 20'' or 16'' barrels and some with no mention of barrel length at all. What does this mean when choosing an ACOG? I'm guessing the increased muzzle velocity and extra 200 yard effective range of the 20'' may throw off the bullet drop marks, but does that mean you NEED to get one configured to your barrel length or it wont work properly?

Also, is there any difference between military and civilian variants?
 

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In for info.  ACOGs get me confused as well.  There are so many of them.
 

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From the Trijicon website

TA31RCO-A4CP: 4x32 Trijicon ACOG® USMC Rifle Combat
Optic (RCO) with Red Dual Illuminated Reticle
The TA31RCO is an Advanced Combat Optical Gun sight (ACOG)
designed for the M16A4 Weapon system (20" barrel). It incorporates
dual illumination technology using a combination of fiber optics and
self- luminous tritium. This allows the aiming point to always be
illuminated without the use of batteries. The Tritium illuminates
the aiming point in total darkness, and the fiber optic self-adjusts
reticle brightness during daylight according to ambient light
conditions. This allows the operator to keep both eyes open while
engaging targets and maintaining maximum situational awareness,
Designed to the exact specifications of the United States Marine
Corps, the unique reticle pattern provides quick target acquisition
at close combat ranges while providing enhanced target
identification and hit probability out to 800 meters utilizing the
Bullet Drop Compensator.

TA31RCO-M4CP: 4x32 Trijicon ACOG® USMC Rifle Combat
Optic (RCO) with Red Dual Illuminated Reticle
The TA31RCO is an Advanced Combat Optical Gun sight (ACOG)
designed for the M16M4 weapon system (14.5 barrel). It provides the
shooter with quick target acquisition at close combat ranges while
providing enhanced target identification and hit probability out to
800 meters utilizing the Bullet Drop Compensator. The TA31RCO
incorporates dual-illumination technology using a combination of
fiber optics and self-luminous tritium. This allows the aiming point
to be always illuminated without the use of batteries. The Tritium
illuminates the aiming point in total darkness, and the fiber-optic
self-adjusts reticle brightness during daylight according to ambient
light conditions. This allows the operator to keep both eyes open
while engaging targets and maintaining maximum situational
awareness. Designed to the exact specifications of the United States
Marine Corp, the unique reticle pattern provides the shooter with
quick target acquisition at close combat ranges while providing
enhanced target identification and hit probability out to 800 meters
utilizing the Bullet Drop Compensator.
 

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Discussion Starter · #4 ·
Yea, I read those.  That's where I got my questions from, the info doesn't really address how exactly they are different.  Most ACOGs don’t seem to be designed with a particular barrel in mind.  So does this mean they will perform the same as the barrel specific ACOGs on all barrel lengths?  If so, what's the point of having different variations?
 

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In short, those little lines under the chevron are slightly different. The trajectory is set up for 62gr 5.56. One for the 14.5" barrel and one for the 20". If you were shooting at a target with a center mass hold on the 300 meter line in the scope using the TA31RCO-A4CP on a 14.5" M4 you would probably hit him in the thigh. Where if you had it on the 20" A4 like it was designed to be mounted on it would hit where you aimed. Does that help a little?
 

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Discussion Starter · #6 ·
Yeah.  That's more or less what I though, but what about the ACOGs that do not mention barrel length?  Are they set up for 16''?  If that's the case, would it really effect the BDC of a 20'' barrel enough to justify getting the dedicated 20'' ACOG?
 

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Steve K said:
Yeah. That's more or less what I though, but what about the ACOGs that do not mention barrel length? Are they set up for 16''? If that's the case, would it really effect the BDC of a 20'' barrel enough to justify getting the dedicated 20'' ACOG?
Well the two listed above are spec'ed for the Marines. It's what they wanted and that's what Trijicon made. My best guess on the others is if it says M16 it's set up for a 20" barrel, M4 = 14.5" and if it doesn't say either I would bet it's perfect for a 16". Again it's just my best guess.
 
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