 |  Magpul MBUS Back-Up Sights - Inset 1 |  Magpul MBUS Back-Up Sights - Inset 2 |
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 Magpul MBUS Back-Up Sights
The front and rear MBUS are made up of three main parts each: the base, the release latch, and the flip-up sight. The front and rear share the same base and release latch, with the flipup portions differing. The flip-up portions are spring loaded and have two notches that retain them in the folded position. The notch is engaged by a hook, or tooth, on the release latch. When the latch is depressed (either by pressing down on the Magpul logo on top, or by using the serrated side extensions), the hook disengages the lock notch and the sight portion flips up instantly. The sight portion is held in the deployed position by spring tension, and is not locked by the release latch. If struck, they will collapse momentarily, then return to the deployed position. Pressing the sight portion back pushes the hook on the release latch down, out of the notch, and the sight portion can be stowed.
Front MBUS - The front sight has two protective ears that are slanted inwards at the top, rather than outwards like the standard M16 front sight, providing a sight picture much like the original Troy sights with the rounded ears. Being made of polymer, the ears are a bit thicker but I didn't find that to be an issue. The front uses a standard square front sight post, which can be adjusted with a 4-prong M16 sight adjustment tool. For each 1/4 rotation, the POI is moved approximately 1-7/8" at 100 meters, based on a 14.5" M4 sight radius. Once sighted in, the sight post can be prevented from rotating by installing a roll pin (two lengths are supplied) to lock it in place. I found the sight post very stiff to turn, so I didn't feel that it was necessary to use the roll pin.
Rear MBUS - The rear MBUS has a windage adjustment knob on the right side that adjusts the POI approximately 3/4" at 100 meters for each click. Both large and small apertures are provided; the small aperture flips forward out of the way, rather than rearward, and can be left down when stowing the sight.
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