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Understanding the USMC new ACOG reticle

The Marines started using a new ACOG reticle in the Squad Day Optic (SDO) on the M249 Squad Automatic Weapon (SAW). That optic got moved to the M27 IAR when the USMC switched over, and now the Corps is having the 4X Rifle Combat Optics (RCO) scopes get this reticle.


Simple, right? Pretty much self explanatory. I feel like I would be insulting your intelligence to explain how to use it.

But, just in case you weren’t clear how to use it, I’ll explain.

First, back ground info:
M249 SAW has been available in various barrel lengths. I’ve seen different numbers thrown around, but 16.3 and 20.5 inches seem to be the official lengths.
The M4 and M4A1 has a 14.5 inch barrel, and the M16 series of rifles has a 20 inch barrel.
M27 IAR has a 16.5 inch barrel.

Previously the USMC fielded two different ACOGs, the TA31RCO-A4 (AN/PVQ-31A) and TA31RCO-M4 (AN/PVQ-31B) for the 20 inch rifle and 14.5 inch barreled carbine respectively.

There is a rumor that Trijicon used the same BDC in each scope, but I don’t believe that. I do know that back in 06-07ish, higher ups in the USMC claimed that the scopes were interchangeable. I think that it shows that the level of precision considered acceptable by the USMC allowed either scope to be used.

The SDO optic, adopted for the SAW, needed to be able to work for either barrel length. It used this reticle with green illumination.

Blah blah blah, let us talk about this reticle. I could type up an explanation, but it would be easier for me to copy and past from the USMC own Squad Weapons manual.

First Zeroing:

Ideally you zero at 300m using the tip of the post. If not that, then use the top of the dot at 100m. Reduced range zeroing can be done using the tip of the post at 33m/36 yards for the M16.

Unlike the RCO models which had a Chevron and Bullet Drop Chart (BDC) that went out to 800m, these have a BDC that goes out to 1000m.

Note the narrower lines below the marked lines. We will come back to that in a moment. Those are important.

Ater the 500m line, instead of using a line to cover your target to estimate range, the SDO reticle has a gap. You fit the torso of your target into these gaps to find the distance to them when you are using the 600-1000m section of the reticle.

What are all these smaller lines below the BDC range lines?

As previously explained, we have these 14.5-16.6 inch barreled guns, and 20-20.5 inch barreled guns. The lower smaller line is for the ballistics of the shorter barrel.

This scope had a BDC for the rifle and the carbine (or the Para-SAW and the standard SAW). This lets the USMC have a single ACOG that can work on the M4/M4A1, M16A4, M249 (regardless of configuration), and the M27 IAR.

I’ve shot out to 1000 yards (~914m) with an ACOG and it is far from ideal for that job. But it is far better than using iron sights at that range. While stuffing a 1000m BDC in an ACOG may be idealistic for the one shot one kill rifleman, it very useful tool for the automatic rifleman’s suppressive fire. It is better for our troops to have it and not need it, than the other way round.

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