question on mounting a scope on a flat top ar-15


May 10, 2006, 11:34 AM
does one have to remove the front sight post on an upper like this if mounting a scope?


photo from

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another okie
May 10, 2006, 12:30 PM
It depends on how high the scope is, which is kind of a weasel answer, but true. If you mount the scope directly to the rail, it may be a problem. You can buy risers that mount to the rail and give you a higher platform for the scope.
And some folks want to mount a red dot and be able to see the iron sights as well through the red dot.

I replaced the front sight and gas block on my AR with a G & G gas block that has a folding front sight and rails on the sides and bottom.

Bartholomew Roberts
May 10, 2006, 12:51 PM
Usually the front sight base is not a problem with magnified scopes because it is inside the focal length of the scope lens. You will see a slight shadow in the bottom of the class but that is usually it.

If you are using a a red dot or low magnification scope, then yes, you will see the front sight. However at anything above 3x the front sight base will usually just be a vague blur (if you even notice that).

May 10, 2006, 01:50 PM
so if i put a 4-12 on it, i wouldnt lose any field of view or even notice it?

Bartholomew Roberts
May 10, 2006, 02:04 PM
No, I doubt you'll notice anything more than an extremely faint shadow you can see through in the bottom third of the glass at 4x.

Don't Tread On Me
May 10, 2006, 05:29 PM
Depends how high the optic is mounted. I've found the shadow to be distracting and annoying if mounted too low.

Here's the thing, in order to get a comfortable cheek weld and view through the scope on an AR, the optic has to be mounted pretty high. There's almost no rings out there tall enough to do this unless you spend $$$ for the ultra-tall tactical rings. If you use a riser, the scope will be up around where the rear peep sight would have been. Add the focal length and you probably won't be bothered by the front sight.

If you mount using non-tactical hunters rings, it will get in the way. That's almost a sure thing.

I have a 4x IOR scope mounted on the very tall IOR rings. It is borderline as to whether or not it would clear the front sight post, so I just put a cutting wheel on the grinder and took off the sight post. Dremeled it smooth and then cold blued it. Looks exactly like the Bushmaster varminter gas block. Problem solved. Note: I did this because I was 100% commited to not using back up iron sights on this particular rifle. If you plan on getting a BUIS, keep the front sight post which saves you having to buy one, and just get the rear flip up, and consider mounting the optic up high (which will be more comfortable anyway).

Don't bother getting a front flip up sight unless it is the kind that mounts to a free float tube. People buy the gas block style front flip ups not realizing that if you are shooting a mag or two of ammo in the heat of a situation, you will not be touching that gas block with your bare hands without melting skin.

Something to consider. The standard sight post is faster as it never needs flipping up. Sorry, went off on a tangent there...

May 10, 2006, 05:55 PM
where do you get a riser? is that what its actually called?

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