By: Derek Vail

The Primary Arms ACSS reticule is by far the best sighting system for the modern fighting rifle to date.  It dramatically increases the first round hit probability of even the most experienced shooter at intermediate ranges and even accounts for wind and target speed.  It does all this without the necessity of doing a single mathematical formula on the range or in the field.  Follow up shots are surety and where this “combat” designed optic shines.  What’s the big deal?  First a little context…


The Marine Corps ACOG

Late in 2004 I was a Marine Rifleman preparing to go to war in Iraq.  Your average 13 man squad was armed with M16A4’s, three M203 grenade launchers, and three M249 SAW’s (light machine guns).  Inexplicably to a young Lance Corporal the M16A4 had a removable carrying handle that revealed a flattop upper receiver while the M16A2 did not.  Other than that, the most significant difference between the two rifles was the A4 had a rail system for attachments.  The new upper was interesting but seemingly pointless to me, as Marine Riflemen did not use any type of optic.  Scopes were fragile and pointless as Iraq was an urban fight.  Red Dot optics are battery dependent.  Grunts just need good, dependable iron sights.  But the switch to a rifle with a flattop receiver proved prescient.  This was all going to change.

I and other talented shooters were singled out for additional training in the Designated Marksman course.  The idea was to have at least one, or several DM’s per squad who could use accurate fire to support the squad at distances beyond what the average Rifleman could.  What separated the DM’s and other Riflemen equipment wise would be the issuance of match grade 5.56mm ammunition, and the Trijicon ACOG fixed 4x scope.  This new scope had a very rugged and “grunt proof” design with and integral Picatinny mount.  The reticule had a simple but effective illuminated chevron with a bullet drop compensator out to 800m.  In reality, shots beyond 500m are a bit optimistic with the issued equipment, not to mention proper target identification at 4x during counter insurgency operations.

Marine Corps ACOG reticule

Marine Corps ACOG reticule


The ACOG proved to be so enormously effective in the Global War on Terror (GWOT) at that time the Marine Corps decided to procure ACOGs for all Infantry M4 and M16 rifles.  This was a huge step in the advancement of small arms for Infantry Marines.  For the first time, there was a standardized and reliable “combat optic” across the Corps.  At the time, Major General James Mattis described the ACOG as, “the biggest improvement in lethality for the Marine infantryman since the introduction of the M1 Garand in WWII.”



Every self respecting warrior surely owns his own rifle.  I had purchased my first “fighting rifle” on Camp Lejeune back in 2004.  It was a Bushmaster AR-15 designed as a close approximation of the Colt M4 with a flattop receiver. At first I used the iron sights as the primary purpose for this rifle was range sessions on my own time and at my own expense.  My opinion then, as it is now was that Infantry Marines at the time had a severe lack of live fire training during this time period and still do, but that is another story.  After my second tour in Iraq in 2008, I was absolute in my faith in the ACOG as a reliable and accurate combat optic.  I would buy one for my own rifle.  I was not entirely enamored with the standard issue reticule however.  The enemy is often moving in urban combat and only exposed for a second or two as they dart to and from buildings or across an alley, and the BDC did not have any hold point for movers.  The chevron covered much of the semi exposed threats at 150-200m mark much like an iron sight can when taking long shots with a pistol.  It was just too wide for this very common engagement distance.

While the chevron was adequate, I found much better reticule in the horseshoe reticule.  It has dots that approximate a hold to make hits on runners.  The large hoop makes picking up targets quickly at close range (already hampered due to 4x magnification) faster than the chevron.  The center dot made firing on targets at the all so important 120-200 meter/yard distances almost too easy as a partially obscured target would not be covered like the chevron would.  In fact, place the head of your threat between the 300m post and the bottom edge of the center dot and you have a headshot every time.

My current ACOG reticule

My current ACOG reticule

My only real complaint however remains that center dot.  Its size is 2 Minutes of Angle (MOA) and I would have preferred something a little more precise.  I actually find it significantly more precise to make hits at 300m with this reticule than at 100m due to that very sharp “post” that is your hold point for 300m shots.  However this ACOG and horseshoe reticule has remained my preferred go-to fighting optic for a decade now, and remains on my Patrol Rifle.


The Advanced Combat Sighting System

After Bull Creek Strategic got off the ground a little over a year ago, Frank and I started building relationships with other companies in the industry.  In particular, finding good quality equipment suggestions for our students on a personal budget can be difficult.  The ACOG is a great example as it has a rather high price point and this keeps many civilly owned rifles from being topped with one, and I would rather our students have 10,000 rounds on their iron sights than 2,000 rounds on an ACOG.  But I digress…

Primary Arms is one such solution.  They have a series of 1x-6x and 1x-8x variable power scopes that start at under 300 bucks that have pretty good battery life, and decent glass.  Variable power scopes of this type have a huge advantage over the ACOG as they are more suited for close engagement.  When dialed to 1x, these types of scopes can act as a red dot and are much faster than fixed magnification scopes such as the ACOG.

The big standout from Primary Arms when it comes to optics is the ACSS or Advanced Combat Sighting System reticule that these scopes sport.  I have mounted the Primary Arms 1x-6x ACSS on my NY (Compliant) Rifle and it has been performing flawlessly.  The ACSS similar to the reticule in my ACOG and retain those leads for runners, and the “death donut” for fast 1x target acquisition.  But the ACSS has some huge and significant improvements.

  1. The Center dot has been replaced with a small chevron.  The tip offers a small and precise aim point, without obscuring too much of the target, like the chevron of the original ACOG.

  2. An illuminated Bullet Drop Compensator, with dots representing a 5 MPH full value wind lead for the respective distances.

  3. A height ranging scale, used to determine the distance of a standing 5’10” man. 

The diagram below shows how the reticule is used for leading runners, ranging an IPSC target by shoulder width, and ranging an upright individual by height.



There are a myriad of other ways to experiment with the reticule to determine distances.  If the threat is sitting or squatting, place the ranging scale on his hip and divide the indicated range by half.  For example, if the top of his head reaches the six when he is sitting, then target him with the 300 yard subtension (crosshair) on the Bullet Drop Compensator. 

The Crosshairs on the BDC represent 18 inches at each respective distance.  This works with everything.  How far is that compound with a truck parked out front?  Well if I know that those stock wheels on that truck are 17”, that’s pretty close to 18”.  I can range it with the BDC and still be close enough to make a center mass shot when the threat does present itself.

The height scale represents 5’10” at those distances.  Can I see the refrigerator (typically 67” to 70” tall) through the sliding glass doors?  If it indicates a 5 on the scale, that kitchen and anyone in it is about 500 yards away. Be creative and use objects that have “standardized” or close-to-standardized dimensions.  Just remember that with 2nd Focal Plane optics, the ranging reticule is only accurate at the highest magnification setting.  For my scope I need to be dialed to 6x to accurately determine distance.

For those with some familiarity, this may sound like we are encroaching on the realm of precision rifle work or the equipment and skill sets of a sniper.  While related, this is not a “sniping” application and most assuredly not what the ACSS reticule is designed for.   What we are talking about here is stretching the effective range of your defensive rifle, with a reticule optimized for firefights where threats are moving fast, only momentarily exposed and partially obscured, and you don’t have the time to use that laser rangefinder or do mathematical calculations with the MIL reticule on your spotting scope.  While this reticule is great for making that first shot on an exposed and unaware threat, it is better suited for quick, multiple target engagements as threats appear throughout a dynamic and changing scenario.

On Zeroing

The ACSS reticule is listed as multi caliber.  The scope that I have is marked for .223-5.56/5.45/.308.  While we all know these calibers have different ballistics they are similar enough that they will work with this optic. Primary Arms has a chart showing generally how to zero the rifle for your particular caliber.  That being said, the holdovers may not be exact and you need to take your rifle, ACSS optic, and cartridge of choice and fire it at actual distance.  Zeroing the Black Hills 77 grain OTM with the point of the chevron at 100 yards, the round impacts a little high at 300 and 400.  Whatever your round of choice an barrel combination is, prove your holdovers after zeroing.  You may find you want to change your zero.  For heavier bullets like the Black Hills 77 grain, you may want your zero a little high at 100 yards.  I found zeroing ¾ of an inch high at 100 yards yielded optimal holdovers for my NY Recce Rifle with the Black Hills ammo.

Current Offerings

The ACSS reticule can be had in a variety of optics.  For this 2nd focal plane reticule you can choose between a 1-6x or 1-8x variable power scopes.  There are several caliber offerings as well.  One covers 5.56/5.45/.308, another for .22 LR, and yet another for 7.62x39/.300 BLK.  I have not met, or heard of an individual who carried the ACOG into battle that hasn’t seen this reticule and agreed that this is the reticule that should have been in the ACOG.  Well, Primary Arms is doing that too.  If you are hell bent on a Trijicon ACOG with it’s proven combat record, one can be ordered from Primary Arms with the ACSS reticule.


When all is said and done, I still have not found my "ideal" optic.  For a long time the ACOG was it, but with the advancements and red dot like effectiveness at close range of 1-6x variable power scopes that is definitely the path ahead for me.  What I have now found however is the perfect reticule for a fighting rifle sporting a magnified scope, the ACSS.  A 1-6x with ACOG like illumination and toughness would be the ticket. Perhaps Primary Arms will drop the ACSS reticule into some Trijicon AccuPoint scopes as they have with the ACOG's.  If they do, I'm first in line gentlemen.