To me, it seems to offer everything an ACOG offers (with different means of illumination) for hundreds of dollars cheaper ($1020 when not on sale)... I see ACOGs all over this forum, but have yet to see a single OS 3.0. Searching here on CGN, a few guys have tossed in a post giving it a thumbs up, but any kind of review has been illusive.... google, youtube turn up nada.
The OS is a very tall sight and almost bulky, because they decided to stick a tall finger adjustable turret at 12 oclock and put a plastic rail in front of it. This means it is almost too tall to mount a mini reflex. Worst of all, it cuts down situation awareness as it cuts off even more peripheral vision than the old C79(because of the giant rubber cover). You have to dip the rifle even more to take a look what it is ahead of you, or somehow extend you neck more at prong position. It sucks when wearing a helmet while the flak vest is fighting to keep the helmet down.
Furthermore, ACOG is lighter and have a smaller foot print. The after market mounting hardware for ACOG is also more robust and more zero repeatable than the single thumb screw of OS 3.0. The exposed finger adjustable turrets on the OS 3.0 are also asking for trouble in the field as a general issue sight.
The OS 3.0 could be a great sight for KD shooting on a flat range. But for the above reasons, ACOG and the fix 4X Elcan Spectre ( FIST sight ) are more preferred than the OS.
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