5.56 Timeline

Aimpoint LRP Mount

I had an Aimpoint T-1 laying around I wanted to use on the B&T APC9K. But I needed a mount to use. I saw a used Aimpoint LRP mount for sale cheap, so I picked that up. The LRP mount is a quick detach throw level mount. Looks like they run about $120-130 new.

I was a little surprised that there is a little tab on the lever of the LRP mount. You have to pull up on the lever to get it to open.

I wonder if crud/dirt/debris would get caught in opening area by the cam. Would probably be pretty easy to clean out with a brush.

I think that little tab makes it hard enough to open that it will not accidentally open on you. Gives it a good bit of security. There is a not so a little hex knob you can use to adjust the tension on the LRP mount. The knob on this one can easily be turned by hand when the lever is open. Don’t turn it when mounted as you can damage the mount.

Aimpoint’s LRP mounts are low profile, but they can come with spacers to raise the height of the sight for guns that need it like the AR15. Sometimes the LRP mounts are sold with out the spacer, so if you need it, make sure it comes with one. You will also need longer screws to use with the spacer, so if you buy used, make sure it comes with those too.

I initially ran into a little issue mounting and removing the mount, but it turned out to be user error. The lever needs to be fully open for mounting.

I’ve not used it enough to know if it hold zero when removed and reattached, or how durable it is. For the price I paid for this one I am plenty happy, but I wouldn’t pay MSRP for one. At the full price, I’d rather buy something else.

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.

How the Israeli’s use the TA31i ACOG

Previously I wrote about the TA31i ACOG that the Israeli’s use:

Quick recap, it is a 4x ACOG with a different reticle than the normal fare.

I was really curious about the markings and zeroing on this model ACOG. Recently I learned about how it was used.

Their TA31i ACOGs were mounted on ARMS quick detach mounts. This allowed them to switch between the ACOG and a night vision scope. The intent is that the night vision scope could be used at night out to 300m, and the ACOG as a day/night optic out to 500m.

The Israeli’s use a 250m zero on their rifles. They sight in 4 cm low at 25 meters using 62 grain ammo. This is suppose to give the following ballistics:

Distance (m)Drop (cm)

I was playing around the numbers in JBM ballistics and I am unable to recreate this reported trajectory.

There are pictures out there of this optic being use on rifles with 11.5, 13, 14.5, 16, and 20 inch barrels. Sometimes the optic is mounted on a flat top. Some times it is mounted on a rail installed on a carry handle. I wanted to find and post up some of these old pictures. But unfortunately I did not save a copy to my computer, and I think they were hosted on photobucket or tinypic or the like. They appear to be gone.

When I plug numbers in JBM ballistics, using 4 cm low at 25m on a M4 firing M855 would have the impacts constantly low. I just can’t see how these numbers work. I wonder if this was calculated from when the IDF was using 13 inch barreled rifles with carry handles.

Anyways, back to the topic at hand. Let us look at that reticle again:

The IDF designated marksman, sharing his notes, explains that the vertical lines on the far left and right of the reticle are for range finding using the size of a human head. The two longer vertical lines are the height of a human head at 200m. The shorter line is the height of a head at 300m.

They continue to explain that the width of the line between the two longer vertical lines on each side represents the shoulder width (commonly 19-20 inches) of a man at 400m.

The line between the shorter vertical line and the longer vertical line on the end is that shoulder width at 500 meters.

Now on a normal ACOG, the lines in the bullet drop chart represent a 19 inch wide width at the respective range in meters. This Israeli marksman was taught that on the TA31i ACOG that these lines represent the length from a persons back to chest (if they were facing perpendicular to you). So you have two ways to range a torso at 400 and 500m and a way to find the range if you can see the targets head at 200 and 300m.

I have a good many mixed thoughts about this information. No offense to the marksman who provided this information, but the trajectory numbers seem questionable to me.

In one way, I really like how you can range a head at 200-300m with out pointing the gun directly at the person. If you had their head lined up with one of those left or right ranging lines, the muzzle will be pointing a fair distance away from the individual.

When using this scope, I found I really liked having the horizontal line as it felt like it increased speed and ease of use. But I missed having a defined aiming point for 100m.

Bonus Mini Optic Tool of the Week: Troy Sight Tool

I had debating posting this up and seeing if anyone could guess what it was, but as far as I know, there are less than 6 that exist. Many of you would have immediately guessed it was a sight tool, but as to what sight, that would have been random luck.

The tool it self is very simple, a knurled piece of aluminum, 4 stainless pins, and a sling stud so you can put it on a lanyard or key-ring.

So what is special about this?

Long ago there was this company that made flip up sights for the AR15. They were called Troy Industries. Their flip up sights were considered the best and a necessary upgrade for a flat top rifle. No one would have considered having a serious use gun with out a quality metal BUIS. I used one of their rear sights while I was in Iraq. It is for this same rear sight that I got this tool for.

Now, I recall Troy Ind had multiple gaffs leading to a boycott of their products. That is probably why you have never heard of them, as we all know how effective conservative boycotts tend be. The last few Troy Industries products probably sit in the back of closets and in boxes in basements. No one would want to be seen with one of their products now. Certainly, the boycotts against Netflix and Walmart by conservatives will cause them to go out of business the same way.

But back to the tool. Early Troy rear sights had a stainless pin that locked the windage adjustment in one of the holes in the windage knob. You had to depress the pin each time for each “click” of windage. This was a pain in the ass, so someone started making these tools with the intent to sell them.

As it always tends to work out, as soon as someone comes up with a business idea, someone else pulls out the rug. Troy redesigned the sight to use a ball detent instead, changed the hole pattern, and included a slot so that it could be adjusted with a coin. Now you could easily adjust a Troy rear sight. Rendering this tool not only unnecessary, but completely useless for the new Troy sights.

Optic Mount of the Week: Scalarworks LEAP/MAG

Old annoying mount

Previously I talked about the Samson Aimpoint 3X magnifier mount I had. It was a minimal viable product. Sharp edges I cut my self on, repeatedly. When open it just sort of flopped around. It was very slow to attach or remove from a rifle. Quite frankly, it sucked. It made me not want to use the magnifier I own. This month I had decided to buy several of the items I wanted, and to sell of a bunch of stuff I wasn’t using. One of the items higher up on that list was a replacement for that damned Samson mount.

I was looking around at the multiple of options and quite a few people said that the Scalarworks mount is the very best. Once I saw the price tag, I had figured it had to be the very best since it was one of the most expensive options. I was pretty hesitant to shell out the money for it. If they are going to charge that much, it had damn well better be the best option out there.

This mount came vacuum sealed in a box with a clearly printed instruction card, and a hex drive torx wrench for the screws.

The ring is hinged at the top and bolted at the bottom. This makes for installing the magnifier very easy.

Instead of a cross bolt or throw level, Scalarworks mount uses a flush ratcheting knob. It is easy to use and the clicks are very positive. Loud too. The clamp is captive so it won’t come apart when you remove this from a weapon.

Lots of laser markings on the bottom. Looks like the individual units might be serialized.

Using this mount, like the factory Aimpoint mount, will require you to remove the rubber from the front of the Aimpoint magnifier cover. Don’t forget to degrease the inside of the ring and the outside of the magnifier before installation.

Putting the magnifier in the mount was very easy.

You can install the magnifier in the mount either direction, so you can have it flip left, or flip right. The clamping wheel will be on the side opposite of which it flips.

The Scalarworks LEAP/MAG mount is very quick to install or remove. Just give the knob a few turns. Not as fast as a throw lever, but fast enough.

The mount is very simple to use, and extremely small and light.

As for the flip to side, it is awesome. Unlike the sad and floppy Samson mount, this one has two ball detents securing it in the open or closed position. It takes a firm movement to flip the magnifier. Not hard, just firm. I can shake the rifle with the magnifier in place or flipped and it won’t move. I can pick up the rifle by the magnifier and shake it with out it moving out of the position it is in. Only with rotational movement then I can easily flip it in or out of place.

Now I haven’t used all the options out there, so I can not say if this is “the best” option out there. But it is damned good. I am glad I sold that old floppy Samson and upgraded.