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Small Arms Collimator (SAC)

The Small Arms Collimator (SAC) is a precision optical device that allows military or law enforcement shooters to confirm zero and/or re-zero weapons, to a high level of accuracy, without live fire.

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The Critical Importance of Accuracy in a Zero Confirmation Device

Boresight devices, which are inherently inaccurate, are considered by some to be ‘good enough’ for zero confirmation in the field. The logic, which makes perfect sense on the surface, is that a given weapon platform does not require a zero confirmation device that is accurate beyond that platform’s capabilities. Using this logic the M4, as an example, which is commonly considered to be accurate to about 4 minutes of angle (MOA), would only need a 4 MOA capable device to check zero. If we consider this logic more carefully, though, its fallacy is quickly exposed. Adjusting zero based on an inaccurate boresight device degrades the overall accuracy of the weapon system.

If we accept that the M4 is a 4 MOA rifle, then we would expect that at 100 yards a good shooter with a stable position would have a 4 inch shot group; all rounds would impact randomly within a 4 inch circle with the center of the circle being mean point of impact (MPOI). If the weapon is perfectly zeroed, then MPOI will be aligned exactly with point of aim (POA). At 200 yards, the cone of dispersion (size of the circle) would increase to 8 inches (see Figure 1), at 300 yards to 12 inches, etc. This dispersion around the point of aim is the result of expected (and, arguably, acceptable) imperfections in the weapon, ammunition, and sight.

M4 Cone of Dispersion

Figure 1

Similarly, if we are using a boresight tool that’s accurate to 4 MOA (which is more accurate than any boresight we’ve encountered, especially in a field environment) then we’ll have a 4 MOA circle representing the deviation of mean point of impact from point of aim. The blue circle in Figure 2 illustrates this 4 MOA circle at 200 yards (more simply stated, the blue circle represents possible locations for the center of the yellow circle in Figure 1). Deviation within the blue circle will be random and, as a result, completely unpredictable. The yellow dot and circle in Figure 2 demonstrate one possible location for MPOI and the resultant cone of dispersion. The large red circle, which is 16 inches in diameter, includes all possibilities and thus indicates the cone of dispersion for an M4 that is ‘zeroed’ using a 4 MOA boresight device. If we ‘zero’ with a 4 MOA boresight, the M4 becomes an 8 MOA platform.

Figure 2

So what happens when a soldier heading out on a mission uses a boresight to ‘zero’ a weapon that, for instance, had the sight removed for cleaning? Maybe the yellow circle falls near the center of the blue circle and he gets solid first round hits. But it’s just as likely that he’ll end up with the yellow circle in Figure 2. The immediate result of that, obviously, is that the enemy may walk away from the fight- or stay in the fight longer- and continue to be a threat. The longer term and less obvious result is that the soldier’s confidence in his weapon and in the training he received is eroded. Our soldier’s likely response over time will be to worry less about shot placement and, instead, to simply increase volume of fire. Applied force-wide, encouraging or allowing the use of inaccurate boresights to ‘zero’ weapons institutionalizes poor marksmanship and forfeits the advantages in accuracy and speed that our weapon platforms provide over enemy systems. The only thing worse is to not conduct frequent zero checks at all.

There are two alternatives to this situation. The first is to ensure that soldiers conduct live fire confirmation of zero prior to every mission. In a perfect world, this is an ideal solution. In the real world, though, it is difficult to implement because of logistical and operational constraints. Some FOBs or COBs, for instance, may not have space for a range. It also fails to give soldiers the ability to check weapons mid-mission, which may be necessary if weapons are banged around or if changing operational conditions (i.e. nightfall) dictate changing sights. Not having this anytime/ anywhere confirmation capability is the reason that thermal weapon sights are often used as handheld viewers, or that warriors are sometimes forced to fight in a CQB environment with a less-than-optimal powered optic.

The second alternative is to use the Small Arms Collimator (SAC), a solution that is both practical and proven. Figure 3 shows the cone of dispersion at 200 yards for an M4 zeroed using the SAC. The blue circle illustrates the possible POA/ MPOI deviation of the SAC, which is guaranteed to be accurate and repeatable to better than 1 MOA (‘repeatable’ means that all SACs of the same model can be used interchangeably with the same level of accuracy). The green circle represents all possible round impacts- the cone of dispersion- when the SAC is used. The outer red circle shows the cone of dispersion using the 4 MOA boresight, for comparison purposes. The improvement provided by the SAC is obviously very significant. Figure 4 provides the same comparison at 300 yards, where the difference becomes even more pronounced. The British Army, by the way, is reporting that 75 percent of their engagements in Afghanistan are taking place at over 170m (185 yards) and that 50 percent are at more than 340m (370 yards).

Figure 3

Figure 4

Failing to check zero routinely or using an inaccurate boresight device to check zero diminishes the capabilities of our weapon platforms. This is ground that we can’t afford to give up, especially given the extended engagement ranges that our warfighters are encountering in Afghanistan. The unique accuracy of the SAC makes it the only tool capable of confirming zero in the field without compromising the speed and accuracy advantage that our weapons provide over enemy systems. Its simplicity and the speed with which it can used (zero confirmation can easily be accomplished in less than 60 seconds), the fact that it doesn’t need a down range target or emit a visible signature, and its proven ruggedness and reliability make it a practical solution that can be quickly and easily implemented.

For a PDF copy of our tis article on the Critical Importance of Accuracy in a Zero Confirmation Device, CONTACT US

Go to The Small Arms Collimator article.
Go to Why Use the SAC article.
Go to SAC Grid and Reference Points article.
Go to Using the SAC for Training/ BRM article.
Go to Using the SAC in the Operational Environment Article.
Go to Collimator vs. Laser Boresight article.

Go to the SAC product page.
Go to the SPA Defense SAC product page for GSA sales.

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