Optical sights have become the sighting option of choice for most firearm applications. It’s been a long time in the making. While optical instruments of various types had been in use centuries prior, it wasn’t until the 1830s do we have a formal, written account of their use. The Improved American Rifle was written in the 1840s and discussed their manufacture. A number of designs came out prior to the Civil War. Despite being a delicate technology still in its infancy, optics were used by both sides.
While optical sights found regular military use by the mid 1800s, they were limited to precision use for sniping only. For over a century optical sights remained too delicate for common issue. It wasn’t until the 1980s that optical device became common issue and standard service rifles. The Austrian Steyr AUG and the British SUSAT mounted on the SA80 were among the first to be general military issue. Other countries quickly followed suit. We did as well.
Trijicon Advanced Combat Optical Gunsight
Starting in 1981 with an Occluded Eye Gunsight in 1981, Trijicon makes a variety of optics for military, law enforcement, and individual shooters. The company introduced their TA01 4×32 Advanced Combat Optical Gunsight (ACOG) in 1987 and the sight was included in the U.S. Army Advanced Combat Rifle program. While the ACR program ultimately did not replace the M16-series, the ACOG found its way into general issue. The ACOG was first used in action during Operation Just Cause in Panama in 1989 and then during Desert Storm. It has remained an issue optic ever since and is offered with a host features.
The original TA01 is still offered, remains an issue optic, and is preferred by many marksmen. This base model is a 4×32 optic built in a rugged aluminum body. Originally designed to wedge and mount inside the carry handle of an M16A2 with a peep in the base to allow use of the as-issue sights, the optic is now found with a Thumbscrew Flattop Adapter (TA51) for mounting directly to Picatinny rails. The reticle is a combination bullet drop compensator and range estimation device. Each aiming mark is spaced for the typical drop of .223/5.56mm cartridges in 100 meter increments. Once a proper zero is established each 100 meter increment from 100 to 800 meters has an aiming mark with no need to adjust the sights. The horizontal stadia subtends 19 inches at the marked distance, which is the average distance across the shoulders of an adult human. The horizontal aiming stadia closest in width to the silhouette simultaneously gives an good range estimate and aiming mark for hold over at that distance. The optic contains an internal tritium illuminator that gives the reticle a red glow in low light conditions.
The other commonly-issued ACOG variant is the 4×32 BAC line, specifically the TA31F. Externally, the only obvious difference is a red fiber optic running diagonally along the top. This is a dual illumination system. The sight uses the fiber optic to automatically increase reticle brightness as the ambient light conditions are brighter. The reticle becomes more dim as the available outside light is lower. In low light or darkness, the tritium insert keeps the reticle illuminated.
Internally, the primary aim point is a chevron reticle, appearing as an open-bottomed triangle. The base of the chevron is 5.53 MOA subtending 19 inches at 300 meters. Just inside the base of the chevron is a vertical stadia line with horizontal aiming and ranging aim points in 100 meter increments marked from 400 to 800 meters, each one again covering 19 inches at their respective distance. Zeroing at 100 meters using the top tip of the chevron for an aiming point established the BDC out to 800 meters. Where the open base of the chevron meets the top of the vertical stadia is the 300 meter aim point and 400-800 continue below.
American Defense ADM ACOG Base Mount, Medium Height
$98.58
Price accurate at time of writing
- American Defense Manufacturing AD-B2 Modular Base, Standard Lever, Black
- Does not require proprietary tools for adjustment
Bindon Aiming Concept
BAC stands for Bindon Aiming Concept, named after Trijicon found Glen Bindon. With binocular vision, both eyes see an image and the brain process views from both into a single image. Different things seen by different eyes can be superimposed into a single, combined view. Red dot reflex sights work best with both eyes view down range and the sight is brought up like a heads up display. The aiming eye sees the aiming dot and the other eye continues to view the scene with the brain imposing both views together.
A good way to learn efficient use of a red dot reflex sight is to block the objective lens, thus blocking the aiming eye’s view of the target. While the aiming eye can only see the dot, and the other eye can continue to see the target but not the dot. When done correctly, the brain superimposed both images together and dot simple appears floating in space onto of the target. The concept was first noted with the Armson OEG sight as that sight required it for use as the aiming tube is closed off at the objective end and can not be seen through.
The Bindon Aiming Concept combines this with a magnified optic. It had been thought that magnification prevented this, however, Bindon noted that using the same approach with reflex sights such as the OEG worked under magnification. A higher power makes the apparent movement greater and blurs the seen, but the non-aiming eye remains on the target. As the sight approaches the target, it slows down, reducing the movement and making it easier for the aiming eye to pick up. This lets a shooter derive the speed benefits of a reflex sight with the precision benefits of magnified optics. An illuminated reticle can enhance this, which is why it works with red dot reflex sights.
GG&G Accucam Quick Detach ACOG Mounting Base
$127.26
Price accurate at time of writing
- Body Material: Solid billet 6061-T6 aluminum alloy
- Body Finish: Type III hard coat anodized matte black per Mil-Spec
- Accucam Material: Solid billet 4140 steel
- Accucam Finish: Manganese phosphated matte black per Mil-Spec
- Weight: 4 oz
Optical Sight Benefits
G. David Tubb notes in his book Highpower Rifle that conventional competition are shooting contests, not seeing contests. The round bullseye targets used in such matches are on large, white boards purposely set up to be easily seen. The SR, SR-3, and MR-1 targets used at 200, 300, and 600 yards respectively all have an aiming mark six minutes of angle in diameter.
For shooting purposes, good iron sights give up very little compared to optics when used on well-defined targets. Comparing the scores winning the Wimbledon (any/any match rifle) and Leech (iron sight-only match rifle) cups at the Long Range Nationals reveals little difference at these 1000 yard matches. Similarly, the National Highpower Match Rifle record of 2396-161x (out of 2400 points possible) shot by Michelle Gallagher was shot with iron sights. NRA rules have had a so-called Tactical Rifle class for years allowing match rifle shooters any sight option desired but the records set with iron sights continue to hold.
With issue gear, the U.S. Army’s Squad Designated Marksman course allows provision for using both iron sights and optics for a combined qualification score. In running this course for hundreds of deploying Soldiers selected and trained as Designated Marksmen, it was common to have shooters fire better scores with iron sights than optics.
This certainly does not mean that optics are a disadvantage. This only points out that good marksmanship has much more to do with shooter skill than equipment. Only novices believe optical sights offer some massive advantage toward shooting ability.
Where optics start to offer notable benefits is field shooting. Targets in the field are rarely as convenient as large, perfect black circles placed on barn door-sized carriers with a white backdrop. Such targets are great for testing marksmanship as they are purposely designed to eliminate variables against good shooting, but they are not good for teaching shooting at erratic targets at unknown distances against natural backgrounds. Enemy soldiers and hunted prey might even deliberately try to hide from observation or from being shot. An optic helps the shooter discern objects and targets in such environments. Lighting conditions, irregular backgrounds, and poorly defined targets quickly become difficult to put iron sights to consistently and an optic helps. It doesn’t improve hold and trigger control, instead, an optical sight brings the sights and target into a single focal plane and magnifies the scene, making easier to discern.
When I attended a training seminar hosted by Trijicon, Marines in the class said the reason the Corps was pushing the M150 (Trijicon TA31RCO-A4CP 4×32 BAC Rifle Combat Optic) down to every rifleman was observation benefits. In urban environments, many unknown contacts were noncombatants but all needed to be identified to weed out hostiles. For many squads, the designated marksman was the only person with an optical sight and squads were becoming overly dependent on one person to identify potential threats for an entire squad. In addition to the TA31 dual-illuminated chevron, the Marine’s ACOG features a horizontal mil scale to give correction for observation and fires. Yes, you sometimes here the self-appointed “old guard” griping about new recruits and current Marines qualifying with optics. While there are good reasons to train with iron sights, the marksmanship skills used are the same. The USMC uses well-defined targets on Table 1 of their known distance qualification that all Marines shoot. A skilled shooter shouldn’t have much difference in score between iron or optical sights on that course. The ACOG shows it’s own at unknown ranges against varied targets against a natural or irregular backgrounds.
Maximizing the Use of Your Trijicon ACOG
A commonly heard gripe against BDC reticles is that they’re imprecise and can’t be adjusted. It’s true that BDCs can’t be adjusted, at least not by the shooter. Here’s the low down on ACOG BDCs.
While most Trijicon 4×32 .223 pattern reticles (TA01, TA11, and TA31) are set for 55 grain bullets out of a twenty-inch barrel when mounted to the carry handle, the TA01NSN was designed specifically for the US Special Operations Command SOPMOD M4 Carbine and that reticle’s bullet drop compensator and range finding stadia lines are based on the trajectory of the 62 grain bullet from a 14.5 inch barrel. The TA01B and TA11C were designed for the 7.62mm, 20-inch barrel, 168 grain bullet, and M16/AR15 carry handle mount. The ranging reticles for the 4×32 BAC line, such as the TA31F, are calibrated for .223/5.56mm flattop rifles. Trijicon can change the reticle pattern in their scopes but must do so by installing a new prism at their factory.
The U.S. military has three bullet weights issued in 5.56mm. While 55 grains aren’t common, the M193 cartridge is still floating around the system and is often more accurate than issue 62 grain. M855 is our take on the NATO SS109 specification and its 62 grain, green tipped bullet is most commonly seen. Mk262 is a 77 grain load based on competition ammunition commonly used in Service Rifle competition such as at Camp Perry. Needless to say, there an enormous number of other options for individual shooters, especially those that hand load.
Even without changing bullet weights, there can be slight differences between different lots of ammunition, one of the reasons manufacturers print their lot numbers. Even with specific ammunition coming out of the same can, a change in environmental conditions such as temperature and elevation also changes points of impact at distance. So a fixed BCD can never be absolutely perfect.
Of course, these changes are dictated by ballistics and change the same regardless of the sight used. A precision shooter tracks these various condition changes in a data book and uses that information to dial sight changes into the sights. Good BDC sights can use the same idea. Shooters in the U.S. Army Reserve Marksmanship Program compete in Service Conditions or Combat matches as held throughout NATO. These events were created by the Commonwealth countries and have a large following in the United Kingdom, Canada, and Australia. The premise is to shoot a variety of competitive courses using only as-issue weapons, ammunition, and equipment. No modifications or “match gear” is allowed.
Using an ACOG, or other good BDC-based sight, it’s best to establish a solid zero that maximizes the reticles effectiveness. Trijicon recommends a 100 meter zero. It’s best to follow that from a prone, magazine-supported position at a MEASURED 100 meters. This is confirmed in full kit as directed by the match. Once this is set, the idea is to never use the adjustment knobs. In practice, there might be a tweak needed as data is compiled. A common joke is that a good shooter is 95% zeroed within 2-3 rounds and then uses 200 to 300 rounds to refine that last 5%. In other words, a good marksman firing and calling the first round can make a bold correction that is close, well inside typical Army or Marine zero standards. A couple rounds more finishes this up. However, matches are won and lost with V or X counts. Where qualification standard is “good” with a hit anywhere in the silhouette, competition demands greater precision. Getting it so that first group fired cold is always centered in the V-ring on demand, and not merely somewhere inside that relatively small area, is the last refinement and takes some work. Especially considering this is done with issue rifles and ammunition which isn’t as consistent as we’d like.
Data is gathered based on the reticle position. The marked stadia may not yield perfect point of aim to point of impact at distance. Just as a shooter with a click adjustable scope records data for sight setting at various distances, the ACOG shooter plots hold points. Rather than a book with numbers corresponding to click values, these are plot sheets with pictures denoting hold points for various distances. In addition to the obvious use of each 100 meter increment aiming reticle, some shooters also plot the relative location of the 100 meter reticle (TA01) or chevron base (TA31F) for all distances. The idea is they want an image of an ideal hold using the largest, most obvious portion of the reticle. For example, for 300 meters a shooter might note where inside the helmet of the Figure 11 target does the 100 meter reticle fit for centered shots. After a run down, shooting while fatigued, or under tight time constraints, it might be best to know where to toss up the largest reticle and still land good hits.
* Prices accurate at time of writing
One thing to note about this “discrepancy” between the reticle and actual point of impact. Team shooters keep track of this because of the precision required during competitive events. This isn’t center of target hits, but center of the center of chest hits. The five ring on some of these targets, and certainly the V ring on all of them, are smaller than the thoracic cavity. Hits that are “dead center” on a qualification course are losing points in a competition. It should be noted that this “error” won’t be apparent to most Marines and Soldiers as the point of impact is still close enough for solid silhouette hits, certainly good enough for a better-than-Expert qualification on either of their qualification courses.
Some competitors enhance this precision approach by adding a rear peep sight aperture to their ACOG. Hole reinforcement labels are adhesive rings sold as stationary for reinforcing pages in a three-ring binder. Carefully centered on the ocular lens, this provides a “rear sight” for the reticle. Now, the ACOG is a good optic and doesn’t have any parallax issue. The idea is that keeping the reticle centered inside the peep when aligned on target ensures that the head is kept in the same place, with identical pressure on the comb of the stock, eye perfectly centered when viewing the reticle superimposed on the target. It’s an additional check to further enhance precision. Self-proclaimed tactical shooters and other whiners like to point out such things aren’t “realistic.” Well, their definition of “precision” is much degraded in comparison. Team shooters use this as a training aid as it forces a better, more consistent position when used in training. Some choose to compete with their additional peep as their presentations for speed shooting become so consistent that the reduced field of view poses no hindrance. When the rifle tracks more consistently and smooth into position, and the head keeps the eye centered behind the sight, shooting speeds up as well. At any rate, the ring can be immediately removed if needed. Some choose not to bother. It’s just a tool that has proven helpful for some.
Lastly is dealing with that old devil wind. Precision shooters have usually clicked a correction onto their sights based on the distance, wind speed, and direction. Wind charts for a given type of ammunition based on ballistics data proved a pre-plotted solution for this. BDC reticles don’t have this provision, however, the ACOG has something that helps. Rather than think of minutes of angle for correction, combat shooters use hold points. That is, section the width of the target into quarters and extend out as needed. For example, hold point zero is dead center of the target. Hold point one is half way between the center and the target’s edge. Hold point two is the edge of the target. Hold point three is another quarter target chuck of distance off the target’s edge. Hold point four is half the target’s width off to the side, etc. The ACOG reticle readily facilitates this. Given that the width of the aiming reticle is the same width of a silhouette at the marked distance, the vertical portion of the stadia line splits this in half. Each half of each horizontal section is half a target with. This is useful in determining hold points. Using this, wind charts are then marked in hold points rather than minutes of angle for wind correction at each distance.
While optics do not increase marksmanship skills, they can enhance the ability of a skilled shooter to obtain hits, especially in a field environment. The U.S. Military has been using Trijicon’s ACOG for years and with great results.
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