Do the bolts on the sight have the magpul logo on the bolt head?
This may or may not be true, I looked at my sights and the heads do not have the logo on the bolt head.
I read somewhere that magpul has their logo stamped on their bolt heads.
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I had a buddy who bought a counterfeit mbus gen 2 set on eBay by accident. His loosened under recoil because the screws didn't have the nylock thread locker applied to the threads. They even had a fake logo on the top, but the release wings on the sides lacked the stepped texture of my authentic gen 2 set. Mine have been abused like a mother and are still quite solid.
Where did you buy yours from?
If they look like any of these, they're counterfeit:
http://www.aliexpress.com/wholesale?...archText=mbus+
Notice the blurred out logos...
We also do not sell the MBUS 2 as a set in a box.
For giggles, I ran a set of PTS ones on a .22lr setup - they're golden on there (actually had a Bushnell holosight poop the bed, but the PTS-MBUS still held). Even the actually MagPul branded airsoft ones are good - the outright counterfeits in the other hand just plain suck. Buy them from a legit retailers, and they'll be solid - you'll be surprised how few complaints about magpul products actually pertain to real Magpul products; and with real stuff the lengths the MagPul CS department will go through to resolve stuff is staggering.
i got my sights via ebay. just buy from a trusted seller like ecop!
i have a couple of sets of PTS on air rifles and while not nearly the quality of the genuine articles i bet they would still work on a 5.56 ar with no problems.