Is there a known problem with recent production MBUS sights?

My new S&W M&P came with a set of the gen2 plastic flip ups and the front sight doesn't like to deploy.  The rear sight is fine, but the front will only deploy if you press on the middle "button" or both of the ears at the same time.  It will not deploy if you only press one side.  I mounted it backwards to get around this in the mean time, I went back to the LGS where I bought the rifle and they didn't have any MBUS to swap out for me and wanted me to send it in.  Rather than do that, I just went to the local Cabellas and bought a new MBUS front to replace it (was going to stuff mine in the package and return it as defective.  Shady, yes, but I didn't want to be without sights for X amount of time).  Anyway, karma caught me and the sight I bought is also defective.

Its almost like either the spring is way too strong or the plastic is too weak.  The whole tab flexes rather than press down and it just won't deploy, no matter how hard you press.


I was thinking of saying screw the plastic and just buying the Pro sights, getting Magpul to warranty the MBUS, then just selling them once they get back...

so you are saying you bought 2 defective MBUS's? i would have to question that.

I'm wondering if there might be something amiss with the rail where the MBUS is being mounted.  If it is too wide or otherwise out of spec, it may be putting lateral pressure on the sight and causing the mechanism to bind on one side.  Just a thought.   One way to check would be to temporarily move it to a much different place on the rail, maybe even back on the upper receiver just in front of the rear MBUS and check to see if it deploys properly. If it does, then the problem is with the rail and not with the Magpul  front MBUS.

I have a Gen 2 MBUS.  It was first on a quad rail and worked fine.  I removed it and placed it on the front of a Daniel Defense MFR 12.0 free float modular rail, and it deploys fine.  Make sure that is in the middle of a rail slot and not pushed up against the shoulders of the slot.  Something is binding and the chance of two MBUS having the same issue seems remote.

OP:  Here is the PDF file with installation instructions from Magpul.  It is important to note that the front sight must be in the UP position when you install it, and that you follow the instructions carefully about the correct tension to tighten the screw-cross bolt and nut.

Well, I'm saying the MBUS that came with my rifle was defective and the MBUS I bought locally was defective.  Improbable, but possible since the examples came from 2 different states and thus were far removed from the same parts lot.


I tried installing it on the receiver and the sight still does not deploy properly.  The starboard side paddle will deploy if you really mash on it, the port side paddle will not deploy at all.  The paddle will clear the indexing tab on it's own side but will barely move the tab on the opposite side.  There is a LOT of flex in the plastic.

Interestingly enough, my sights don't have the allen screws like the PDF.  The only have slotted screws for a flat-head driver.  I've been using a quarter as a tool so I don't over-tighten them.




But while messing with my AR more I'm really thinking that the deployment mechanism on these sights is going to interfere with mounting options for my flashlight.  I might want to look for alternative sights anyway.  I like Magpul, I think they make quality stuff, so I'm looking at the Pro series sights.  Looks like they're on the cheaper side compared to Troy's and others out there, and I like the tool-less front sight...
On that subject, are there any suggestions for more slimmed down BUIS?