I have a Burris FastFire III on an ADM quick detach mount that I'm putting on my SCAR17S - I'm wondering if there are any advantages to mounting the optic closer to the front or the rear of the rail.





I've searched online, and there really aren't any good answers - in fact there are some contradicting assertions of fact. Some experts say the dot gets larger the further away the optic is places from your eye, so keep it closer for more precise aiming or place it further out if you want faster acquisition at closer ranges.














 

It is not critical.  Remember that with irons, it is your front site that you actual bringing into focus.  The rear sight provides the alignment through its otherwise invisible aperture.

Just play with it until you are happy with the perceived size of the dot and your optic's field of view, which will diminish as you move the dot farther from your eye.

My amateur guess is that all said and done, you'll probably end up with it at the equivalent of where it would be on your AR,  just a bit forward of your trigger.

Nice rifle!

Thanks! I like it.

 

There is no right answer.   The consensus seems to be pretty far forward, reason being that the housing obstructs less of your FOV around the optic (both eyes open of course).

Another POV is to mount it as far to the rear as possible maximizing the FOV through the optic (again, shooting both eyes open).  This is helpful with multiple targets and situational awareness as it is better/faster to transition from one target inside the optic FOV to another vs. having to bring the next target from outside the FOV to inside.

I was in camp #1 until recently, I read a thought provoking article by a LE trainer about mounting it to the rear.  I tried it rearward mounted (Aimpoint micro, against the rear BUIS) in a carbine course and like it a lot better.  I'm making up numbers to go with my subjective observations but it seems like I get about 33% more FOV through the optic and it only obstructs my vision around it maybe an additional 10%.  It definitely isn't linear, I have way more FOV inside the optic with very little noticeable obstruction by moving it rearward (again with a micro, results may be different with a larger PRO/M4).

Personally, I'd mount that little Burris all the way back against the BUIS.

I guess it could be scientifically tested, get a range with many targets at different distances. Mount optic forward and count # of targets inside FOV and # visible outside.  Then mount it to the rear and repeat.  Simple math would yield the percentage increase inside the FOV and if any were not visible due to the housing obstruction at either mounting point.

Thanks for the thoughtful post - I have heard arguments to that effect. I haven't done any extensive shooting at a course. I carried an ACOG in Afghanistan, which is a totally different kind of optic.



For now, I've mounted the sight further forward:

 

It doesn't matter a whole lot.   Farther forward does give you a little less obstructed vision with your aiming eye, which isn't a big factor for both eyes open shooting.    Regardless of where it's placed forward or back the dot will be come into and go out of view under the exact same circumstances.  The FOV argument is misguided, sure the window is larger but that doesn't mean the dot is visible more often.  

I run mine farther back but only because it's slightly less likely I'll bonk it on something if it's closer to my face.

On 1 power optics far enough away that you can't see the sides of the inner tube or housing.  Start close and you will see the inner sides, move away till you can't see it.  For my Aim Point Micros that is at the far end of the reciever with nose to the charging handle.




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Not sure what you mean by this?  The larger FOV, the more forgiving it is of head position making it easier to pick up the dot in the optic.  The larger the FOV, the more targets will be visible through the optic.  Taken to the extreme, placed at the eye, the dot would always be in the FOV and all targets would always be inside the FOV as well.

I have an MRP so I can place my optic wherever I want. It started out over the forward edge of the mag well and I've crept it back since, settling on all the way back.  

I really like the Gen 2 Delta Point, thinking about getting one for my M1 Carbine.

I like the EOTech closer to me to take full advantage of its already large lens. With the EOTech switched off, and using the BUIS, the field of view with the irons is great. They are both zeroed at 50.

I think you are comparing apples and oranges - check out the pics I've posted.



You are running an EOTech on an AR15 with an A3 upper and stock round handguards. You have at most 1.5" of "wiggle room".



I am running a smaller red dot on a monolithic upper - I have around a foot of space.



I am asking the question because I have options - most people are running the optic closer to their eyes because that is their only option.

 

Basically you don't need FOV exactly, only to see the dot, which is in the center of that window.  There's a difference between eyebox (where my head must be relative to the rifle's orientation in order to see the reticle or dot, and FOV.  We want wide FOV to see stuff magnified around a scope reticle, but with a 1x optic FOV isn't helpful in that way.  We only need to see the dot.  It's like a front sight post, it's like the dot is attached to the barrel, but way out at infinity.  All that matters is where must your head be to see that dot, and the answer to that is not FOV, but eyebox.

Eyebox is helpful.   Red dots have the dot projected at infinity, so you end up with a rectangular eyebox, not a cone.  A physically larger window like on a EOTech increases the width of that tubular eyebox, and forward/back placement only provides apparent FOV of the stuff around the dot.  

If closeness helped, 99% of us would wear that thing slammed against the back of the receiver closer than an ACOG nose to charging handle, but that turns out not to be the case.

Closeness helps to be able to see the dot from less than ideal shooting positions with a less than ideal cheek weld.  Closeness helps to be able to see more targets within the optic instead of having to transition them from outside the tube.

It isn't a big deal either way though, pretty minor consideration in the grand scheme of things.

Far forward enough to get a magnifier behind it.