Trijiconís New 5.5x50mm ACOG Riflescope


by Jeff Quinn

photography by Jeff Quinn & Boge Quinn

July 3, 2006




The white buffalo was standing still in a clearing about 1125 yards from my position atop a small ridge. This was the very same buff that I had seen a year earlier, standing in the same clearing. It was meant to be.  The New Mexico sun was shining brightly upon the buffalo, and he was easy to see through the scope.  When I had first seen him the previous year, I knew that I would be back to see him again. I had often thought of that buffalo in the preceding months, and now, I had him in my sight. I had never fired at anything at that long of distance before, but I had confidence in my rifle, ammunition, and the scope. My ability was the only thing concerning me at the time, but I had a steady rest. The rifle was a DPMS .308 AP-4. The scope was a new 5.5 power ACOG from Trijicon. I had used ACOGs before (see previous articles here and here), but they were smaller and of lesser power. The optical clarity of this new ACOG was much better than I had expected, even on a glass as expensive as this ACOG.

The Trijicon ACOG is the scope of choice for many of our nationís elite military forces. I know that in Iraq, soldiers are trying to get one on their M4 carbines any way that they can.  They have other optics available, but will trade off an Aimpoint for an ACOG at the first opportunity.. They are tough, reliable scopes, and are a valuable aid to accurate fire, especially in low-light conditions. I have a couple of other ACOGs on AR-15 rifles, and they have never let me down. One of my favorite endearing features of the ACOG is that it needs no batteries. Trijicon uses tritium to light the aiming point, so it is always "on", always ready. Some of their models also feature their BAC illuminator which brightens the reticle according to the available light conditions. This also uses no batteries, and it offers a good bright aiming point in sunlight, but produces a much fainter aiming point in low-light conditions, just as is desired. It works automatically, and perfectly, and the new 5.5x50 ACOG has this feature. Trijicon offers the 5.5 power ACOG with the reticles calibrated for either the .223 Remington (5.56mm NATO) or .308 Winchester (7.62x51mm NATO) cartridges. The one reviewed here is the TA55A, which is set up for the .308 Winchester cartridge, and includes the flattop adapter, to allow easy mounting on any Picatinny rail, such as on the DPMS AP-4 carbine to which I attached the ACOG. This ACOG comes with a nylon case, and a scope cover. Like all ACOGs, the housing is made from forged aluminum, and it is waterproof to 100 feet. It is one really tough scope.

The reticle on this ACOG is calibrated out to 1200 meters, and is very easy to use. With most scopes, shooting at long range requires the use of a special scope base with built-in elevation. The ACOG does not. It is entirely useful from as close as a few feet, out to 1200 meters. There is no need to turn turrets or adjust anything after the scope is sighted in. Just aim and squeeze the trigger. Simple. The reticle looks like this:

I lifted this image from Trijiconís web site to better illustrate the reticle. The results of my attempts at taking a picture of it through the scope were not too good.  After sighting in the ACOG, I found that the aiming points were pretty darned accurate using Lake City military ball ammunition. I fired at varying known ranges on silhouette targets, and the aiming points were pretty much dead on.

As an aside, I also tried out a new duffel bag while playing around with the DPMS AP-4 rifle. This bag is called the Big Foot, and it certainly is a versatile bag. The one that I used was their medium size, and it was huge. It could hold the rifle, extra mags, ammo, scopes, lunch, and a small adult all at the same time. The versatility is in the ability of the bag to be unzipped, making for a good prone ground cloth or tarp. Most of the time, I did not even bother to fully unzip the bag, preferring to lay upon it closed, adding another layer between me and the rocky ground.  If you are in the market for a good drag bag, duffel, or any versatile utility bag, check them out at:

Back to the ACOG, the 5.5mmx50 is larger than other ACOGs that I have tried, with a length of twelve and one-eighth inches, and a weight of one pound and nine ounces. It also has superior optical quality to any other ACOG that I have used. It is a very bright, clear, easy to use scope. 

Returning to the white buffalo, my brother Boge was spotting for me. Like I stated, I had a pretty good rest, and was somewhat confident in my ability to hold the rifle steadily. I held the ACOGís reticle on the "10" crosshair, which represents 1000 meters. The wind was howling atop the small ridge from which I was shooting, gusting in the afternoon New Mexico heat to about forty miles per hour, but thankfully it was at our backs, and the wind seemed relatively calm out in the small clearing where the buffalo stood. I squeezed off the shot. It takes about two and one-half seconds for the bullet from the AP-4 to travel 1125 yards. However, after what seemed like much longer, Boge shouted "Hit!" He seemed a little surprised that his older brother had made the shot, so I fired again. Another hit. For the next couple of hours, Boge and I fired many more shots at that steel buffalo, hitting a lot more than we missed. The DPMS rifle and the TA55A ACOG made it easier than I would have thought. We also fired at several other of the NRA Whittington Centerís steel silhouette targets that day, including life-size mule deer, antelope, and black bear at ranges from 600 to 800 yards. The rifle/scope combo performed admirably at all ranges.  The ACOG had plenty of magnification for the targets. I see no need for higher magnification, unless the targets are much smaller, as in varmint hunting. The ACOGís performance exceeded my expectations, and really changed my perspective of the scope. I had thought of the ACOG as only being useful for military type situations, but now see it as an excellent hunting optic as well.  We also fired at rocks of various sizes at both known and guessed-at distances, with very good results, along with the sighting in chores on paper targets.

The TA55A ACOG scope is a tough, durable, easy to use aid to accurate shooting at any distance, and seems to be the perfect choice for the DPMS .308 rifle. It is not inexpensive, but quality never is. The ACOG is a top choice of our nationís elite military forces. If it meets the needs of those who stand in the gap for us, I think that it will serve me, and you,  just fine.

Check out the entire line of fine Trijicon products online at:

For a closer look at the DPMS AP-4 rifle, I refer you to my previous article in our ARCHIVE section, or go to:

Jeff Quinn

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Click pictures for a larger version.


Trijiconís New 5.5x50mm ACOG Riflescope.



Jeff tests the 5.5x50mm ACOG at the 2006 Shootist Holiday, held at the NRA Whittington Center near Raton, NM. In the bottom picture the "white buffalo" is too small to be seen, but it is located at the center of the tiny clearing at the edge of the timber line.





The ACOG's calibrated reticle is very clear and easy to use.









The Big Foot bag is huge, rugged and versatile.