The aperture/post iron sights on an M16 were designed to perform, and for combat sights they are fast on target. Shooters soon discovered, however, that a flattop AR was more flexible. An optic ranging from a red dot and reflex sight to a variable power scope made the operator more lethal. Like all mechanisms, optics can fail.

Back-Up Iron Sights (BUIS) allow an operator to stay in the fight even if his or her primary optic is inoperable. BUIS are made to be deployed in an instant if they are needed.

Here’s a look at 11 BUIS to invest in.

American Tactical Flip Up Combo

The Flip Up Combo sight is an all metal front and rear sight set design for use on AR platforms. The rear sight has two apertures and is fully adjustable. The front sight has an adjustable post. Both sight stow flat and mount to any Picatinny/Weaver style rail. (americantactical.us; 800-290-0065)

BlackHawk Folding Sights

Minimalistic and simple, the spring-loaded, push button-actuated folding sights lock into a stowed position until needed. Utilizing a hybrid polymer base and aluminum body design for high weight-to-strength ratio, both sights are compatible with mil-spec sights. The rear sight features a single “hybrid” aperture, while the front sight’s circular hood protects the sight post. They are available in Black, OD Green and Dark Earth. (blackhawk.com; 800-379-1732)

Command Arms FFSFRS

At under an ounce the FFS (Folding Rear Sight) and FRS (Folding Rear Sight) are lightweight. The super low profile allows them to be added to a weapon without snagged on gear. They are made of polymer and steel. No tools are needed to adjust elevation or windage. The spring loaded deployment button is ambidextrous. Square lug in mount means no wiggly when mounted in a Picatinny rails. (commandarms.com; 215-949-9944)

Diamondhead Polymer Flip-Ups with NiteBrite

Both the front and rear polymer BUIS have NiteBrite photo luminescent inserts that glow in the dark and can be charged by natural light or with a flashlight. They are spring loaded and flip-up and stay up securely with a push of a button. The front sight is adjustable for elevation without tools. (diamondhead-usa.com; 413-739-6970)

Dueck Defense RTS Sight System

The RTS (Rapid Transition Sight) System was designed by top 3-Gun shooter and IPSC Grand Master Barry Dueck, and are suitable for competition or LE/military tactical shooting. They are off-set and help increase an operator’s ability to hit near and far targets. Made of 7075 aluminum, they are ultra durable and are the same height as mil-spec iron sights. They mount to the top rail and will not interfere with a mounted optic. (dueckdefense.com; 714-349-9638)

Magpul MBUS Pro

The MBUS Pro sights are all-steel with a corrosion resistant hardened finish. The rear sight features a dual aperture and is windage adjustable with a low-profile knob with positive detents. Wings protect the adjustable front post, which has a knob to adjust elevation. Both are standard AR height when deployed. Mounts on any mil-spec Picatinny/STANAG rail. (magpul.com; 877-462-4785)

PRI Delta Rail Mounted Flip Up

The PRI (Precision Reflex Inc.) Delta flip-ups are constructed of T6-6061 hardcoated anodized aluminum. The sight is designed to lift up and lock in the upright position. A pivot pin is pressed to fold the sights. They weigh less than two ounces. (precisionreflex.com; 419-629-2603)

Promag AR-15/M16 Flip Ups

A spring-loaded release is pressed to raise and lower the Promag rear and front sights. The rear sight has two apertures and is adjustable via a knob. The front sight has an adjustable post that is protected by wings. Both are made from T6 aircraft-grade aluminum and have a black phosphate mil-spec finish. Both mount to most Picatinny/Weaver rails and are secured with a knurled thumb screw. The front sight can mount to a railed gas block. (promagindustries.com; 800-438-2547)

XS Sight SYSTEMS Xpress Threat Interdiction

The XTI angle mount sights feature a Big Dot Tritium front and a shallow V white stripe vertical Express rear sight. The sights are properly aligned when the Big Dot of the front sight rests on the vertical post of the rear sight, dot the lowercase i. Visible in low light conditions, sets are available in Tritium front only or 24/7 Tritium front and rear sights. (xssights.com; 888-744-4880)

Yankee Hill Machine AMG-250

The AMG-250 sights feature AmeriGlo tritium inserts for better target acquisition in low-light situations. The front post has a glowing dot and the rear sight has a dot at 9 and 3 o’clock around the aperture. It fits standard AR sights and aftermarket models that have a post and aperture set up. (yhm.net; 877-892-6533)

Yankee Hill Machine Q.D.S. Same Plane Sight System

Push a button and the Q.D.S. (Quick Deploy Sight) system automatically deploys. They are extremely lightweight being constructed almost entirely out of aircraft-grade aluminum. The front sight mounts on the same plane as the rear and is available in either post or hooded. Both sights attach via a clamp to a rail. (yhm.net; 877-892-6533)