Optimal Height for RDS on AR?

[Tensaw]

What do we think is the optimal height for a (mini/T2) red dot on an AR? I will disregard absolute co-witness and look at 1.56” (lower 1/3); 1.93”; and 2.26” (Unity FAST mount); and the latest entry, 1.70”. Talk about splitting hairs...

The use case is average dude trying to protect hearth and home (and/or Truck Gun) - no NV nor gas mask in the mix. I wish I could try each of these out, but alas, that is not in the cards. I am mostly torn between the 1.93 and the 1.70 with the 2.26 seeming like a bridge too far perhaps - but I don’t know what I don’t know.

And would it make a difference if we were running the T2 on an AR pistol vs. Carbine?

[DpdG]

Most of my time is on lower 1/3rd, although I have one "pistol" set up around 1.70" so grain of salt- Take into account use case.
- 2.26" is very tall and probably more applicable for NVG/mask usage, but it's so high irons can run under the optic (Unity mount has built in irons).
- 1.90" is still quite "heads up" without being quite as far weighted towards mask/nvg, but also precludes any sort of irons use with the optic mounted, as the sighting plane is basically right through the mounting surface of optic/mount (QD optic or offset irons required if irons are desired).
- 1.70" is more of "not squished on buffer tube" vs "heads-up" and technically allows use of irons through the optic, but barely (only the tip of the front post is visible). Does not provide the degree of clearance for mask/nvg that higher mounts do.
- 1.56" is lower 1/3. It's basically the default for a reason.

Ultimately there is no "optimal" but rather use case and taste dictate the weighting of strengths v. weaknesses. Personally I'm starting to go towards 1.70" for general purpose and would like to try 2.26" for with mask/nvg, but still haven't made the jump due to cost and (un-experimented) concerns about height over bore/offset at distances significantly inside the zero.

[frozentundra]

If using a fixed front sight rifle, I like to be able to roughly index the front iron sight through the tube like a giant ghost ring. This is still quite doable with a lower 1/3 if you get used to your holds. I've never tried it with taller mounts.

This is just in case battery dies, optic dies, optic inadvertently turned off by mistake, brightness setting incorrect for conditions, dot washed out by bright lights, low sun angle creates lens flare...all that kind of crap.

[dontshakepandas]

Most of my time is on lower 1/3rd, although I have one "pistol" set up around 1.70" so grain of salt- Take into account use case.
- 2.26" is very tall and probably more applicable for NVG/mask usage, but it's so high irons can run under the optic (Unity mount has built in irons).
- 1.90" is still quite "heads up" without being quite as far weighted towards mask/nvg, but also precludes any sort of irons use with the optic mounted, as the sighting plane is basically right through the mounting surface of optic/mount (QD optic or offset irons required if irons are desired).
- 1.70" is more of "not squished on buffer tube" vs "heads-up" and technically allows use of irons through the optic, but barely (only the tip of the front post is visible). Does not provide the degree of clearance for mask/nvg that higher mounts do.
- 1.56" is lower 1/3. It's basically the default for a reason.

Ultimately there is no "optimal" but rather use case and taste dictate the weighting of strengths v. weaknesses. Personally I'm starting to go towards 1.70" for general purpose and would like to try 2.26" for with mask/nvg, but still haven't made the jump due to cost and (un-experimented) concerns about height over bore/offset at distances significantly inside the zero.

I think this is a pretty good place to start.

I'm 6'2" and I definitely prefer a more heads up position for use with a dot. I like the 2.26" over the 1.93" since I can a) still have usable BUIS and b) use the Unity FTC magnifier mount which is excellent. The only downside is the mechanical offset, but it isn't anything some practice can't overcome. If you don't care about BUIS and aren't running a magnifier and are used to lower mounts a 1.93 may be a good place to start.

[theJanitor]

I'm 100% on unity height (2.26") as it allows me to look squarely through my glasses and nods

eta: there are no top rail BUIS options for non-micro footprint optics, at FAST height

[Default.mp3]

eta: there are no top rail BUIS options for non-micro footprint optics, at FAST heightOne could put said optic on a QD mount, and pair it with a FAST Riser, though. I have irons on my 11.5" with a FAST Riser and EXPS-3, and if I pop the EOTech off, the irons handily clear the riser. Just something to consider, as even if you don't get cowitness, you still have useable BUIS.

I'll also note that both absolute and lower 1/3rd are a pretty broad terms, frustrating enough, between different companies. Absolute cowitness will run from ~1.4" to ~1.5", while lower 1/3rd will run from ~1.5" to ~1.7" (1.7" specifically called out is pretty new, but as a general lower 1/3rd height is nothing new, ADM's lower 1/3rd has been 1.69" for ages).

As for the actual "best height", it really does depend on your physical measurements/abilities, as face shape, height of cheek over shoulder, neck flexibility, etc. will all play a role in the "ideal" height, not to mention a million other factors (how your gear is set up, shooting style, etc.).

If you really wanted to mess with heights, perhaps grab some cheap Amazon mounts and risers to play with? Alternatively, look at what mounts have the best intersection of price, features, and perhaps compatibility with other accessories (primarily magnifier mounts), and go from there.

[Tensaw]

Yeah, for whatever reason, I tend to turtle up and go nose-to-charging handle as a default - which I am consciously trying to break out of. Even shooting shotguns, I will bloody my nose with my thumb knuckle every once in a blue moon. I’m 6’4” so there is no good/valid reason for doing this. (I blame Jeff Cooper who, through his writings, sold me on the notion of having the lowest possible scope/bore offset possible.)

DpdG laid out the pros and cons better than I did, but I have looked around at what the pros have to say (Cowan et. al.) They really like the Unity mount - and for good reason, but a lot of that seems to coincide with their use of NV and rail-mounted lasers. I may have to get over myself and go with the Unity mount.

[Tensaw]

One could put said optic on a QD mount, and pair it with a FAST Riser, though. I have irons on my 11.5" with a FAST Riser and EXPS-3, and if I pop the EOTech off, the irons handily clear the riser. Just something to consider, as even if you don't get cowitness, you still have useable BUIS.
If you really wanted to mess with heights, perhaps grab some cheap Amazon mounts and risers to play with? Alternatively, look at what mounts have the best intersection of price, features, and perhaps compatibility with other accessories (primarily magnifier mounts), and go from there.

I actually did buy a very cheap riser from Midway. That thing sucked. So tight on the rail, and then so hard to tighten with the fastener, I was afraid of damaging my upper. And then I wasn’t sure what height I was mimicking. That lasted for all of about five minutes before I ditched it.

But yeah - cheap imitations abound. Somewhere I came across a thing showing where some outfit had ripped out the Unity mount right down to the logo. I may cast about and see what I can come up with.

ETA: Sure enough, there are Unity knock-offs on Amazon for about $35. That said, I would probably be money ahead just buying the real deal and then selling it off if it didn’t work out.

[DpdG]

Forgot to add this to my first post- as a broad guideline, the taller the mount, the less comfortable it is to use prone. Whether that matters or not is a personal decision.

[theJanitor]

One could put said optic on a QD mount, and pair it with a FAST Riser, though. I have irons on my 11.5" with a FAST Riser and EXPS-3, and if I pop the EOTech off, the irons handily clear the riser. Just something to consider, as even if you don't get cowitness, you still have useable BUIS.


Yes, I should have said there are no "see through" BUIS options. Using the XPS (non-QD) won't get to the 2/26" height. Only the EXPS gets to the 2.26" height, but comes with the built in QD. The BUIS situation with the EXPS isn't an issue for me, just noting for the OP

[M2CattleCo]

I like 1.93 and the Unity height mounts so much now that I consider anything lower to be wrong and you would have to have some deformity or something for it to actually be better.

[Sanch]

Timeline of zeitgeist

1990 - red dot on top of A2 carry handle. It’s all that’s available. Way better than irons. This is amazing!

2000 - flat top uppers common. Absolute cowitness. Nose to charging handle, baby! Same cheek weld as irons but get a sweet red dot in case your position is a little off. Irons visible through optic for *when* the red dot fails

2010 - lower 1/3. Who does nose to charging handle anymore? This isn’t camp perry. Let’s all run BUIS which will still visible through optic for *if* the optic fails

2015 - let’s get 1/4” higher than 1/3 cowitness. And get rid of those BUIS, red dots don’t fail and in the rare black swan event they do, we can caveman through the red dot tube as good enough. Batteries don’t die in the time frame the next generation optic comes out and we replace ours to look cool on the ‘gram. We all have silencers now and need the weight savings by ditching the BUIS.

2018 - Some Tier 1 SF units run Unity 2.26 height mounts. Some civilians get them. Civilians get shit on by PF members who think they’re posers. Those mounts are too high! Do you even filmless white phosphor dual tubes, bro?

2023 - everyone will be running 2.26” height optics when they realize how great the heads up position is. Bringing the red dot height back to where we used to run them in the 90’s on top of A2 carry handles. Such a great new innovation, wow!

[theJanitor]

Even if you manage to fix your timeline, what’s your point and how is it helping the OP?

[Tensaw]

Well, I’ve decided to go with the Unity mount. Waiting on Brownells to get them back in stock. I *really* like the Scalarworks 1.93 mount. I like the QD system (apparently I have commitment issues) and the sleek design - but it ain’t 2.26” so Unity it is. I like the BUIS on the Unity. I plan on using a front flip-up sight with the rear sight built into the Unity mount.

I appreciate the input guys!

[littlejerry]

I've been using a piggyback MRDS over a 2.5-10 NXS for many years now. At first it was strange but it really didn't take long to get comfortable. Now I appreciate the upright head position and prefer it in certain circumstances. The MRDS is the "primary" optic for me out to ~100 yards

[Maca]

I used a Unity 2.26 for about a year and liked it far better than standard lower 1/3rd. I then tried a Scalarworks 1.93 and really liked the design. 2.26 vs 1.93 was negligible for me.

[D-der]

Timeline of zeitgeist

1990 - red dot on top of A2 carry handle. It’s all that’s available. Way better than irons. This is amazing!

2000 - flat top uppers common. Absolute cowitness. Nose to charging handle, baby! Same cheek weld as irons but get a sweet red dot in case your position is a little off. Irons visible through optic for *when* the red dot fails

2010 - lower 1/3. Who does nose to charging handle anymore? This isn’t camp perry. Let’s all run BUIS which will still visible through optic for *if* the optic fails

2015 - let’s get 1/4” higher than 1/3 cowitness. And get rid of those BUIS, red dots don’t fail and in the rare black swan event they do, we can caveman through the red dot tube as good enough. Batteries don’t die in the time frame the next generation optic comes out and we replace ours to look cool on the ‘gram. We all have silencers now and need the weight savings by ditching the BUIS.

2018 - Some Tier 1 SF units run Unity 2.26 height mounts. Some civilians get them. Civilians get shit on by PF members who think they’re posers. Those mounts are too high! Do you even filmless white phosphor dual tubes, bro?

2023 - everyone will be running 2.26” height optics when they realize how great the heads up position is. Bringing the red dot height back to where we used to run them in the 90’s on top of A2 carry handles. Such a great new innovation, wow!

My eyesight's certainly not what it used to be,
I'd been curious about an A2 RDS

[dontshakepandas]

Well, I’ve decided to go with the Unity mount. Waiting on Brownells to get them back in stock. I *really* like the Scalarworks 1.93 mount. I like the QD system (apparently I have commitment issues) and the sleek design - but it ain’t 2.26” so Unity it is. I like the BUIS on the Unity. I plan on using a front flip-up sight with the rear sight built into the Unity mount.

I appreciate the input guys!

WO has the black model in stock at a good price.

https://www.weaponoutfitters.com/unity-fast-micro-mount-black.html

[Tensaw]

WO has the black model in stock at a good price.

https://www.weaponoutfitters.com/unity-fast-micro-mount-black.html

Ordered. Thanks!

[theJanitor]

I'm utilizing the unity FTC magnifier mount, so I'm almost exclusively using Unity mounts for my EXPS and T2. However, there are other brands making high mounts. ADM and others have "NV height" mounts. I've been using the KAC skyscraper mount (2.33") on my SR15 for awhile. It's not svelte, but you can use the BUIS through the mount, and allows for attaching a FTS magnifier at the correct height