Cantilever mounts allow Red Dot Optics to be mounted far enough forward so that a magnifier can be mounted with proper eye relief.
A few weeks ago, a reader emailed to ask for an article regarding preferred Aimpoint mounting locations on carbines. I have always done what just seemed right to me and had never put much thought into it. But apparently there was some method behind my madness, so here are my thoughts on the topic. Note that much of this is based on personal preference, so you may want to adjust to your needs.
The first point of consideration is whether I am mounting a full size Comp M68 or a Micro. The Micro is an excellent evolution of the sight and offers outstanding battery life, durability, in a lighter and more compact package than the M68. However, the viewing window is indeed smaller which, to me, changes some things as to how my eye picks up the dot when I mount the rifle.
M68 Optic
I prefer to mount the M68 as far forward on the receiver as possible. If I plan to use a magnifier, I prefer to use a cantilever mount like the LaRue LT129 Cantilever Aimpoint Mount. The viewing area is large and easy to pick up. I don’t like mounting further forward than the end of the receiver since you can get loss of zero if your rail is not monolithic with the receiver. Also, the optic is now so far forward from your face the dot can be harder to pick up. Add to the fact that mounting accessories at the muzzle end of the gun makes it harder to hold for an extended period of time. Likewise, I don’t recommend mounting the M68 too far back as it precludes the ability to mount a 3X magnifier behind it. Even if you have the rail space, some folks mount the M68 far enough back that the magnifier is just about jammed into your eyeball.
I prefer to mount the Micro series sight just a bit further back towards the eye. Keep in mind this can interfere with usage of the 3X Magnifier.
Aimpoint Micro
The T-1, T-2 and H-series optics are my preference when I’m trying to set up the lightest, handiest guns possible. One of the downsides for me is that the viewing window is smaller than that of its bigger brother. Theoretically, this is not a problem as the RDS is not magnified and can be used both eyes open. However, the smaller window does mean you have less margin for error when picking up the dot because if your head/eye shifts beyond a certain range, the dot is no longer visible. What I like to do is bring the Micro just a little bit back toward my eye, which effectively increases the apparent window size. Just be sure to leave space for a magnifier, if that is a piece of gear you will be using.
Howdy Tim,
great article. We are running the older M68 on our patrol LE6920s. Originally I set them as far forward on the upper receiver but recently ran into a snag.
We are setting up new Tahoes and I requested two gun vertical mounts up front. Well they buy the two gun rifle rack I ask for but low bid gets a different manufacture partition and a different manufacture center console. the three don’t mesh and modifications were required with the gun mount and back cage/partition for the rifle to fit and remove with some finesse required.
I had to move the M68 as far back as it would go, with the optic mount near the rear fold down sight. Based on your post, I think we are ok with the optic so far back but I will stress officers need to adjust the stock to give them the best eye relief based on their body style which may mean moving the stock reward one or two additional notches.
any issues with the optic so far back that I have not addressed?
thanks in advance, MH
There are technically no eye relief issues with a reflex tyle sight. However, mounting it further back can sometimes induce the tunnel vision effect to less trained personnel as they tend to focus in on the dot instead of using both eyes. I totally inderstand the issue of rack compatibility so you gotta do what works for your situation.
I would leave the stock in the same position. No reason to move it back unless their face is physically running into the optic.
Mike, I am an LE Pro Staff guy with Aimpoint, so I see a few of these things.
I am actually a fan of running the optics farther to the rear. This is especially true of the Micro’s. With stuff like my AUG, I have the Comp M4 as far to the rear as I can get it. I find coming out of a low ready to take a shot, the dot hits my vision plan faster as its arc is not moving as far. It helps to stay focused on the target and look through the dot instead of “at” the dot, which is how it should be done. With the bigger optics on an AR I tend to mount them farther forward to clear a magnifier, as I run them a lot. Without a magnifier, I lean towards running them back a bit farther than most. You should have no issues with the rearward set up.
Another issue: DO NOT run parts of the mount partially on the receiver rail and partially on a fore-end rail. On a monolithic like some of the Colts and the LMT’s, it is fine. On guns where they are a two piece unit, you can see a couple minute shift in zero from doing this. The best option is to keep all of the mount on the receiver no matter where it is as far as fore or aft.
I have a lot experience with the M68 while deployed and it is highly effective. I don’t have any experience with the T or H series sights, do you find the trade off worth it? I am thinking about picking one up. My to has always been the ACOG which is great all around but has it’s disadvantages close in.
About a year ago, I asked Greg Ellifritz of Active Response Training this same question. Most carbines I see have the dot sights mounted near the front of the rail, even if they don’t use a magnifier. I wonder if anyone has ever done any testing to determine if sight position affects time-to-first-hit? Testing various locations for the sight and timing might be useful to see if closer or further forward affects dot acquisition time/reliability.
With training, any minute differences would probably be statistically meaningless. However, in my own experience, a smaller windowed sight mounted too far forward could make aquisition less consistent for shooters that dont have a ton of maintenance training on the gun resulting in less consistent head position.
I mount mine as far forward on the receiver as possible, set to absolute co-witness fixed irons. I don’t like moving parts on my rifles so none of this separate magnifier on a swing mount nonsense. If I want magnification I’ll just switch the dot for a fixed 4x, that’s what q.r. mounts are for. Anyway, since I use absolute co witness my head is always down so I have no problem picking up the dot since it’s right there at the tip of my front sight post anyway.
Cowitness is the topic of a separate article. As for QR, I am not a huge fan of swapping optics all the time.but whatever works for your environment, just make sure youve properly vetted your SOP with real world experience. Once that is done, if it works for you, then rock on.
QR Mounts have such a high degree of repeatability now I find it far easier than mucking about with more stuff. Especially stuff that needs to be aligned. Is the cowitness article up? My search-fu is weak. I understand the rationale behind lower third, but I find it more unnatural since all my early training was irons only. When I was younger I’d notch the top of the aperture for close in work, but I can barely see the darn thing now. I think I probably lose some situational awareness with absolute, but old dogs/new tricks for me so far.
I appreciate the article. In reading the forums all the internet commandos say they prefer to run the micros further back but, mount them forward to allow room for a magnifier. It seems like its ‘tacticool’ to run them as far forward as possible.