The TA01NSN ACOG is a classic at this point.  A compact fixed 4x scope with a bullet drop chart calibrated for M855 out of a carbine barrel.  People assume it is calibrated for a 14.5 inch M4 barrel, but every time Trijicon has given numbers it sounds like the Bullet Drop Chart (BDC) was based around a 16 inch barrel.

The main thing that sets the TA01NSN ACOG apart from the majority of the other models of ACOGs are the iron sights mounted on it.

The iron sights on this ACOG are more for emergency use, for example should you manage to break the ACOG, or for use in heavy rain at close distances, etc.

The front sight is adjustable for windage, the rear sight is not adjustable.  This front sight also has a vial of Tritium in it allowing it to be seen at night.  In the past, there have been people who expressed a concern about this revealing their location.  If this is a concern to you, the sight can be removed, or simply taped over.

I’ve found some of the TA01NSN ACOG iron sights to shoot massively off left or right, so you will want to check it out before you rely on them.

Older ACOGs have 1/3 MOA adjustment that requires a tool like a coin to adjust.  Newer ACOGs have a 1/2 MOA capped turret that is tool less.

The adjustment caps on the TA01NSN are not tethered.  On some other models they are.  When I was zeroing this old ACOG, the O-ring used to seal the elevation knob broke apart.  I notice this O-ring is amber, while ever other O-ring on the ACOGs I own (and on the windage) are orange leading me to believe that this was a replacement done by the previous owner.  You can see the failed amber colored O-ring in the picture above.

I have seen the adjustment cap threads cross threaded or stripped from abuse.  While ACOG scopes are tough, nothing is impervious to user error. & abuse.

ACOG adjustments can be very annoying.  First, don’t try to turn the adjustments to the extremes, that can damage the scope.  Second is that the scope adjustments can hang.  The scope is compact due to a prism and the adjustments rely on the prism moving against a spring.  This means that sometimes when you dial in an adjustment the scope prism won’t actually mode until you smack the scope or fire a couple of shots.  Normally this would be considered very unacceptable in a scope, but in this case it is considered a quirk of the compact tough ACOG.

The center of the TA01NSN crosshair is meant to be zeroed for 100 meters.  Then each hash mark represent a 19 inch width (a mans shoulder width) at the distances of 200 to 500 meters.  The very top of the bottom thicker bar is the 600m mark.

The 4x magnification aids in locating and identifying targets.  When used on a rifle with a fixed front sight base the shadow of the base will appear in the field of view.  Personally I don’t think it seems as bad as it shows in the picture, but I know it really irritates some people.

I took this opportunity to try the Elcan Specter DR in 4x mode and the TA01NSN side by side.  For speed of acquiring a target, or moving from target to target I felt they were the same.  I would say the increased eye relief of the Elcan may make it a far better choice for a .308 or other higher recoiling rifle.  But for shooting 4x on a 5.56 I didn’t feel one offered any significant advantage over the other.

A last point, the ACOG scopes have tritium illumination.  There are some newer models that use batteries.  The idea behind the tritium is to provide battery free illumination of the reticle in low light situations.  I’ve found that often when it is dark enough to use the illumination, I can’t see the target.  Since the half life of Tritium is about 12 years, some of the older ACOGs got gotten very dim.  Trijicon will relamp a scope for a price, but it will likely be more cost effective to sell an old ACOG and just buy a new one.

I really love the old TA01NSN, but now variable 1-X scopes are taking over that nitch.  While the newer 1-X power scopes tend to be larger, heavier, and far less durable than the venerable ACOG, the capability they offer are leading more people to choose that over the ACOG.  If you are primarily expecting to identify and engage man sized targets at 100-600 meters the ACOG is hard to beat.  If you need the fastest speed for up close, or precision sub-MOA shooting, look elsewhere.