Scope height on AR-15?

[AZBastiat]

I finally moved one of my scopes to my AR-15 with sales advice from a local gun store. I'm trying to figure out whether the scope height is right. I have an A3-style picatinny upper, to which I've added scope rings. The centerline of the scope goes through the triangular front sight post. This can be seen through the eyepiece as a white haze which clears if I move my head slightly to one side or the other.

If my setup is NOT right, what height should the centerline of the scope be relative to the front sight post?

[jmdavis]

I think 1.375 is the height of the aperature, My mount is 1.4 and is fine.

But I also only shoot the Riflel at 4x+ and due to glare off the front sight tower, I replaced it this week with a low profile gas block. You could always replace yours with a Picitinny mount gas block and add a folding sight.

[sluggo]

You probably are are already aware, but it is important not to bridge the the rail across the barrel nut with your scope- better to use a cantilever mount.
Popular  cantilever mounts have a 1.5 -1.6" centreline height.

[Luminous Rabbit]

I finally moved one of my scopes to my AR-15 with sales advice from a local gun store. I'm trying to figure out whether the scope height is right. I have an A3-style picatinny upper, to which I've added scope rings. The centerline of the scope goes through the triangular front sight post. This can be seen through the eyepiece as a white haze which clears if I move my head slightly to one side or the other.

If my setup is NOT right, what height should the centerline of the scope be relative to the front sight post?

There are two things that concern me about this setup as described.  Obviously there are a lot of details we don't have.

1) The first is that generally rings don't work well as a mounting system on that type of upper.  The scope ends up too far back, and you end up doing the "turtle neck" (opposite of turkey neck) in prone to get into the eyebox.  Sluggo's suggestion of a cantilever mount (e.g.http://www.midwayusa.com/product/2420197402/vortex-optics-cantilever-1-piece-extended-scope-mount-picatinny-style-with-integral-rings-ar-15-flat-top-matte) is the typical solution.

2) Generally speaking for magnified optics you don't want the front sight in the way.  If you do have one, and use a high enough power optic with a big enough objective, it will disappear.  With that kind of scope, you don't need to be above the front sight - the scope literally looks around it.  Since you're seeing a shadow, clearly that isn't happening.  Depending on what lengths you want to go with, you could just deal with it, try a different optic, or replace the gas block on your rifle with a different one that doesn't stick up (plain, railed, or an integral folding front sight).  Each of those options has different implications for how you setup backup iron sights if you want them.

I'll be glad to help if I can.  Posting a picture of your rifle might be a good starting point just to make sure we're all on the same page.

[jmdavis]

One can get a cantilever rail, mount it to the top of the receiver then add low rings (with a 1 inch scope) to get the scope level closer to the height of the aperture on an iron sighted AR.

[henschman]

You will want something in the 1.5" tall range (top of rail to center of ring) to clear the front sight post.  If the FSP is in the center of your scope's FOV it WILL negatively effect image quality, even if the image is magnified to the point that it is out of focus.  You will also want some sort of mount that extends the optic far enough forward while being mounted only to the upper receiver, so you can get in a proper shooting position with a good turkey neck.

Unfortunately a 1.5" tall optic on an AR generally makes it impossible to get a true cheek weld, with neck muscles fully relaxed and the full weight of the head resting on the cheek bone.  It generally requires some neck muscle to get your head up high enough to see through it (unless your face is shaped like Mr. Ed's).  It is even more difficult if you have a collapsible stock that leaves your cheek resting on the bare buffer tube. 

On all my scoped ARs, I have either a low profile gas block under a free float handguard, or a folding front sight base, and I mount my scope about 1.28 to 1.35" above the rail by using a YHM extended Picatinny riser and low rings.  I also use either a fixed stock or a UBR.