Mounting rear BUIS in front of optic

[ruchik]

I have a question regarding the rear BUIS on an AR. Does anyone run the rear BUIS in front of the optic? I have a Vortex Spitfire prism scope with an etched reticle, and I find that the eye relief is a bit too long if mounted forwards of the rear BUIS. I mounted the optic back on the receiver almost as far as it will go, and put the rear sight in front of it. I can still see through the peep apertures just fine with it mounted forwards like this, but I was wondering if there was any reason not to do so?

[MOLON AABE]

https://youtu.be/YhPchsAD-O8

I have had mine set up this way since slightly before swapping my Aimpoint PRO to a Trijicon MRO, I have had no issues with my rear sight mounted in front of my optic, as long as it's mounted on the upper reciever it should be good to go, your sight radius will still be as long as on a Military M4/M4A1 in most cases, and even if its not your sight picture as it appears and works for you is more important than how far apart the front sight is from the rear.

Here's my setup, before Boredom Krylon Disease took effect.

http://uploads.tapatalk-cdn.com/20170106/0c13925f6187826e5a1d3b0c2be11a78.jpg

http://uploads.tapatalk-cdn.com/20170106/89b4a4823891ccd180e00bdb8e8ea332.jpg


Velocitas, Opprimere,
Violentia Operandi

[ruchik]

Hey, I watched that video! It was the first video I watched when looking into this question. I kept asking myself "Well, why not?" and couldn't come up with a good answer. But I figured I'd ask the people with actual experience here, to see if there's additional data points I haven't considered (I've never been in a gunfight, or work with guns for a living).

[MOLON AABE]

With the larger of the two apertures on the Magpul Pro rear sight, and the front sight at the end of the 15" handguard my sight picture is right between what you would see on a M16A4 with the 0-200M and the 300M apertures, sight radius is between the M16A4 and the M4A1.

Velocitas, Opprimere,
Violentia Operandi

[BrigandTwoFour]

I've seen it done. It's not ideal, but I suppose its a workable solution. I'm sure there will folks out there who say that its crazy, though.

I come back to this question, though: is it better to mount the thing you know you will use in the best position that works for you and put the thing you might use in a less optimal position; or to compromise the thing you will use in order to make room for the thing you might use. I've seen the same justification used for removing BUIS from rifles entirely when TA-31/RCOs are involved.

[MOLON AABE]

I honestly cannot think of any real drawbacks to doing this.

Velocitas, Opprimere,
Violentia Operandi

[Koshinn]

It's really hard to use a rear peep aperture if it's far from your eye.

Just try it and you'll see.

That being said, for something like a TA31, I'd mount the ACOG in the best position and do whatever I can with irons.

For a non-magnified optic, I don't see why this is an issue. People are faster on target when the optic is further forward... And with both eyes open, the optic housing doesnt actually obscure anything.

[MistWolf]

People are faster on target when the optic is further forward...

I pick up the dot quicker with the Aimpoint mounted closer to the eye

[JNG3]

The Canadian military does this on their Diemaco/Colt C7/C8's. The eye relief and mount on the Elcan generally prohibits a BUIS from being mounted in a conventional manner, thus they mount their BUIS (when they choose to actually use one) in front of the Elcan.

[dwhitehorne]

I guess if it is your only option. I was taught that the round rear appature close to the eye naturally centered the light. "Clear tip of the front sight post naturally center left to right up and down in a blurry rear sight appature" blah blah blah. We switched the rear sight on the 1903 and have had the rear peep at the back of the receiver ever since. David

[Averageman]

As I've gotten older my eyesight has degraded. Having tried a lot of different things to make up for this has me thinking, what ever works for you is what you go with, what looks goofy to someone else is irrelevant.

[Amicus]

I labored over this for a while. My view became, eventually, that a BUIS forward of the optic can be satisfactory, but not optimal. This became an obsession eventually. The following (see p. 2) shows some of my efforts:

https://www.m4carbine.net/showthread.php?66462-Really-dumb-idea-short-eye-relief-ACOG

I did not end there, and finally found a good way to mount the sight with a BUIS behind it. It is now one of my go-to rifles, but it took a dedicated build to get it there. If you are like me, you will eventually find the BUIS-in-front-of-optic annoying enough to want to do something about it. If I had not really liked the sight (and been a little less stubborn), I would have sold it and gone to something else.

[MOLON AABE]

If it holds zero, the sight picture is acceptable, and you use quality sights you will be good to go.

If it's stupid and it works, it's not stupid, just strange.

Velocitas, Opprimere,
Violentia Operandi

[scottryan]

The Canadian military does this on their Diemaco/Colt C7/C8's. The eye relief and mount on the Elcan generally prohibits a BUIS from being mounted in a conventional manner, thus they mount their BUIS (when they choose to actually use one) in front of the Elcan.



The Buis is not designed to be used in this location.

The Diemaco Buis is designed to be moved rearward when the Elcan is taken off the gun.

[JNG3]

I stand corrected then. I was not aware that the foreward mounted BUIS was essentially in a 'storage' position. This would explain why I've seen countless pictures of C7's and C8's without ANY BUIS mounted. Those soldiers must have elected to store the BUIS elsewhere and not ahead of the Elcan.