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The Big Bad BUIS FAQ

Article by:    "strick909" of

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What is BUIS anyway?
BUIS, or Back Up Iron Sights, come in many configurations. The purpose of a BUIS system is to give the shooter the ability to accurately aim the rifle if the primary optic fails.

What types are available?
Two types are available, flip up and fixed. It is possible to combine the two systems and use a flip up in the rear and a fixed FSB (front sight base) or vise versa.

What is co-witness?
A: Co-Witness is the ability of your irons to look through your optic (1x - not magnified) - so they both shoot on the same trajectory. There are two kinds - absolute (both the dot and irons are on the same plan), and offset (where the irons are usually in the lower 1/3 of the optics display). With co-witnessed sights you can verify the zero of the optic by looking through the irons (the dot should sit on top of the front sight). However, normally you look over the irons and just use the optic (trust me, you won't notice the iron sights); should the batteries fail your head comes down a fraction of an inch and you're using the iron sights (looking through the now-dead optic).

(from the Maryland AR15 Shooters FAQ)

What makes folding BUIS so good?
Some shooters like to use a primary optic (such as an Aimpoint or EOTech) with no visual distractions. The folding BUIS systems would be ideal for this. Other shooters using magnified optics will require a folding rear sight in order to get proper placement of a scope. Many first responders like a folding front BUIS because it is less likely to get hung on something compared to a fixed FSB.

What makes fixed BUIS so good?
First, it is less expensive. Most rifles will come with iron sights and adding a primary optic to an existing system would be the cheapest way to get set up. Also, if you ever need your BUIS, there is nothing to "flip". They are already in place. That means that the time to transition to BUIS from a disappearing red dot is zero.

If I use a magnified optic, won't the FSB be in the way?
Nope. You won't even see it.

What distance should I zero my BUIS?
50 yard IBZ

Where is the best place to buy my BUIS? Who has the best prices?
Please support the dealers who support this site! Check the Industry Forum for a list of dealers and also check the Equipment Exchange for other deals on BUIS and optics from dealers and members of!! All of the BUIS below have a hot link to the original manufacturer. These links are for informational purposes. Most of the time, an dealer will have a better price. However, there are exceptions. Ameetec, Bushmaster, & Cavarms are all supporters, so it's ok to order from them.

What BUIS systems are available?

Note: All images have been reduced to thumbnails for faster loading. Click on an image for a larger view.
(Not all have larger images.)


40L 40A2 (2.0 oz) 40


Ameetec Arms

Front Folding Rear Folding


Bushmaster BMAS

Fixed Rear

Flip-up Rear

Flip-up Front

Flip-up Front Rail Mount


Cavalry Arms

Fixed Rear

Fixed Rear



Fixed Rear Mangonel Front
Flip Up Sight
Mangonel Rear
Flip Up Sight 
Front Sight   



flip up rear
flip up
Tactical Modular
flip up front
Flip up front for
dovetailed gas blocks


Knight's Armament (no link available)

Rear Folding
300 Meter Sight

Rear Folding
600 Meter (2.25oz)

Folding Front Sight
for RAS


LaRue Tactical

Fixed rear sight (QD) (3.0oz)

Les Baer

Front flip up w/gas block


Fixed rear sight

Matech No link

Folding Rear Folding Rear



Front flip up

Troy Industries

Flip up Rear (1.9oz)

Flip up front Rail mount (2.2oz)


Wilson Combat

Flip-Up Rear Sight

Yankee Hill Machine

Gas Block Front
Flip Sight
Forearm Front
Flip Sight
Front Sight
Front Sight
Gas Block


Front Sight
Flip Rear Site Solid Rear Sight


Chopped carry handle (4.9oz)

This chart is courtesy of TheRicker at ADCO FIREARMS