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I have one on my 556 SWAT and it works great. I have only tested the 100 and 200 yard stadia lines, but they appear to work fine. It is one of my favorite combinations.
 

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.....i would do a search on Acog...there's a lot of info in the optics section...

...the short answer is "generally" no...if the optic is calibrated for M855 out of a 14.5 inch barrel...when firing the same ammunition out of a 16 inch barrel...it will develope a greater exit velosity...you'll notice the change in POI in elevation at range...

...BDC reticles are calibrated using a specific cartrage fired out of a specified barrel length at a specific density altitude...usually sea level or 1000 feet AMSL...

...generally...but no always... in .224 caliber this usually means a 14.5 inch barrel using M855 ammunition... there are exceptions...for example...some Acogs are calibrated using M193 ammunition fried out of a 20 inch barrel...

...the BDC reticles are calibrated to compensate for the acceleration of gravity...the degree of bullet drop will depend on it's duration of flight until it strikes the target..."some" important considerations are the muzzle velosity developed in a a particular length barrel...the projectiles ballistic coefficient and the air density...

...mabey these treads will give you some idea...

... http://www.sigarms556.com/viewtopic.php ... light=acog

... http://www.sigarms556.com/viewtopic.php?t=8955

... http://www.sigarms556.com/viewtopic.php ... light=acog
 

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TAO1NSN

Ullie is correct on the use of ACOG's on specific barrel lentghs. But I seem to remember the only scope specically made for the 14.5" barrel is the TA31RCOM4. The most others can be used with either the 16" or the 14.5" barrels. I have a TAO1NSN on my 16" barrel 6920 .have checked out the stadia markings out to 400 yards ane it seems to be right on. I also have a TA31F on my SIG 556 but have only checked it out to 200 yards. Below is a blub on the NSN. Hope it helps.

Trijicon 4x32 ACOG 4x32 Scope TA01NSN w/ Amber Center Illumination for M4A1 fits the AR15/M16 flat-top rifles. Modifications to this Trijicon Special Forces TA01 NSN model include an integral rear ghost ring aperture and a tritium glow-in-the-dark front sight(Amber Illumination) for close-combat/back-up sighting, and includes Flat Top Adapter, Backup Iron Sights and Dust Cover. TA01NSN Trijicon ACOG 4x32 sight was designed specifically for the US Special Operations Command SOPMOD M4 Carbine. To meet their requirements, the reticle bullet drop compensator and range finding stadia lines are based on the trajectory of the 62 grain bullet from a 16 inch M4A1 barrel. The M4 Trijicon ACOG 01's are a compact and ruggedly designed scope and a valuable addition to any rifle - comparable to optical sights issued to British and Canadian Armed Forces. The finest optical design of this 4 x 32mm scope, 100% U.S. made components and Mil-C-14806A multi-layer coated glass elements make the Trigicon ACOG the ultimate telescopic sight. The black daytime reticle in the Trijicon Scope ACOG 4x32mm glows red at night and in low light due to its tritium composition. Forged aircraft aluminum housings - the same material as the M16 receivers - are precision machined and hard anodized to match the finish of the M16. Unique to the Trijicon ACOG sights is its internal adjustment capability - only the prism housing moves - making this the most rugged scope available. The ACOG by Trijicon will withstand exposure to temperature extremes, salt spray, fog, fungus, humidity, sand, dust, shock vibration and a free fall drop onto a hard surface. Aerospace seals make the Trijicon A.C.O.G. scopes waterproof to depths greater than 500 feet. A hole through the M16 integral base permits use of the iron sights without removal of the scope. This Trijicon sight can be attached to the carrying handle with one or two screws (2nd screw is optional). The user does not need to make any special adjustments between shots at different ranges. The ranging is already built into the reticle pattern (parallax free along its vertical axis). The width of the horizontal lines corresponds to the height of a 19 inch silhouette at that range.
 

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Discussion Starter #5
ACOG said it works on the 16inch M4 at 2600 FPS. Whats the muzzle Vel of a Sig 556 with a 62 grain round? Is the barrel set up the same as a milspec M4?
 

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ACOG Reticle

If one hand loads it's relatively easy to get a 62 grain loaded to whatever velocity is required to make at the reticle work. I shoot 60 grain Hornady Spire points at 2750 and it seem to be on up to 400 yards.
 

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Re: TAO1NSN

samnev said:
To meet their requirements, the reticle bullet drop compensator and range finding stadia lines are based on the trajectory of the 62 grain bullet from a 16 inch M4A1 barrel.
...the M4 / M4A1 has a 14.5 inch barrel...not a 16 inch barrel...

...you have ~ 90 / 100 FPS difference in exit velosity between a 14.5 and 16 inch barreled M4 / M4A1 when firing 5.56mm M855 ball with a BC of .304 under standard atmospheric conditions at or near seal level...

...manufacturers...distributers...and gun rags are sometimes incorrect when publishing information...sometimes it's prudent to do a little extra homework...

...the time to target will determine the bullet drop...and in most cases an Acog will get you close enough "as a combat sight"...an Acog is not a precision optic...nor was it intended to be...
 

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Re: ACOG Reticle

samnev said:
If one hand loads it's relatively easy to get a 62 grain loaded to whatever velocity is required to make at the reticle work. I shoot 60 grain Hornady Spire points at 2750 and it seem to be on up to 400 yards.
...if you come close to the external ballistics of the projectile with which the reticle is calibrated...specifically it's trajectory and time to target...you'll be fine...regardless of barrel length...
 
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