The Trijicon ACOG is a legendary optic among many servicemen who have relied upon its durability and versatility during combat.  While I am lucky to count myself among that group, my time spent overseas was spent with the venerable TA01 which has been surpassed time and time again by more advanced offerings from Trijicon.  While researching optics I came across what seems to be a unique collaboration: a Trijicon ACOG using a non-Trijicon reticle.  In this case, it’s the ACSS reticle from Primary Arms.  While I can only speculate as to why Trijicon opened up its flagship optic to using a non-OEM reticle, this seems to be a one-of-a-kind partnership.

Given that we’re essentially looking at two products here, I want to cover some of the basics on each before diving into how they work as a whole.

Trijicon and Primary Arms collaboration | The ACOG with ACSS reticle

First, the ACOG.  The Advanced Combat Optical Gunsite is a compact, fixed power scope of the “prismatic” design variety.  Rather than using a series of lenses (and a long tube), a prismatic scope uses a glass prism to focus the image.  The result is a much more compact scope, though one with a generally shorter eye relief (1.5″ here).  There are a variety of ACOG models with varying reticles, magnification and even power sources.  The specific model shown here is the TA31-R-ACSS.  It has 4x magnification in the aluminum alloy body, with the reticle being illuminated both by (mildly) radioactive tritium as well as a fiber optic cable.  This ACOG is much shorter than traditional scopes and weighs in at 9.9 ounces.  Water-proof, shock-proof and damn near Ranger-proof, the ACOG is the king of the hill regarding short-to-mid-range combat optics.

acog acss
photo courtesy of Primary Arms

The Advanced Combined Sighting System is the patented reticle provided by Primary Arms.  It combines a number of features, intended to provide combat accuracy at extended ranges with little loss of speed.  The four areas of focus are:

  • Bullet drop:

When shooting up close, one finds the aiming chevron surrounded by anattention-grabbingg horseshoe, both illuminated.  This is the section of the reticle intended for use in CQB distances.  Below that is the “ladder”, the bullet-drop compensation table.  While calibrated for M193 ammo through a 14.5″ barrel, slight changes in zero distance can provide “close enough” accuracy in other bullet weights of 5.56mm as well as 5.45mm and 7.62 nato.

  • Windage
acog acss
photo courtesy of Primary Arms

Fairly simple, the dots represent a 5mph wind’s effect on an M193 round at the given ranges.  If the wind is stronger, weaker, or not at full value, simply adjust as needed.  Combat accuracy isn’t the same as precision accuracy.  Getting really close on the first round then adjusting for a follow-up hit is just fine for a rifleman at 712 yards in the wind.  Give the shooter the tools to start out on it or near it and let him do the rest.

  • Ranging
acog acss
photo courtesy of Primary Arms

We’re given two methods of range estimation here.  Target height or target width.  Using the average human torso width of 18″, one can do some simple dividing and multiplying to work out an approximation of range.  Or, using the ACSS, you can simply be thankful the horizontal bars from 400 yards and down match up to an 18″ width.  As shown, the horseshoe is used for 200-300 yard ranging, which isn’t as needed since range estimation errors at that distance are their smallest and bullet drop isn’t nearly as severe.