Quick question about MBUS rear sight

[rbuzz]

I've got a S&W M&P 15 MOE edition with an Eotech EXPS-2 that I like more and more each time I shoot it. It is a great combination that will be even better once I eventually add a magnifier. The question I have is with the Magpul folding rear sight. The rifle is sighted in, with both with the iron sights and with the Eotech. I can shoot with either system and the gun shoots accurately. You can also cowitness the iron sights with the Eotech and everything lines up perfectly.
My question concerns the rear sight. Even when properly sighted in, the rear sight must be adjusted to almost as far to the left as it will go. It shoots great, but I wonder if it is normal for the sight to have to be set so far to one side. It seems that ideally it would be approximately centered. The sight is installed correctly and it came from the factory with that setting, but it just looks wrong, even though it shoots accurately. Has anyone else ever noticed this?

 

[BillyJack2012]

Can you tell if your front sight is canted to the left?

 

[rbuzz]

The rifle has the A2 front sight, and it appears to be perfectly aligned. The sides of the front sight are tapered so it's hard to find a perfectly vertical surface to check with a level, but what I did was to place the rifle in a vise and using a level on top of the picatinny rail, I first made certain the rifle was level. Then I placed a second level on top of the ears of the front sight. Both levels indicated that they were perfectly level. I know that this is a far from perfect method, but I couldn't come up with a more accurate method. No matter which way you look at the sight, it appears to be perfectly aligned. If you can suggest a better method of checking the front sight, I am open for suggestions.

 

[BillyJack2012]

Where did you get the Magpul sight? I ask because at close up, it doesn't look as finished as mine. Are you certain it's not a Magpul PTS sight?

 

[rbuzz]

The rear Magpul sight was the sight that was delivered on the rifle that I purchased new. I have the exact same rear sight on my S&W M&P 15-22 MOE, and they appear to be exactly the same.

 

[BillyJack2012]

Well, then you know it's a legit rear sight. I'd pull the BUIS off of the 15-22 to see if you have to sight it in the same way.

 

[rbuzz]

I did as BillyJack suggested and swapped out the BUIS sights. Using the Eotech as a reference point because the iron sights previously cowitnessed perfectly, there was a very obvious difference in the sight alignment. In order to achieve the same cowitness with the Eotech I would have had to crank the BUIS rear sight over to the left just as the original sight was set from the factory. So it was a good suggestion, but it didn't play out.
The only thing I can think of is as was suggested before, is that the front A2 sight is canted although no matter what angle you look at it, it appears perfectly aligned and my attempt to use levels to check it prove it. Of course it would probably only take a very small amount to make a large difference.
I guess it's something that I'll just have to live with. After all it shoots perfectly as it is. It's just that it seems that the rear sight should be fairly closely centered and the fact that it isn't will still bother me. Thank you BillyJack for your time and ideas.

 

[BillyJack2012]

No problem. I haven't seen too many canted sights on M&Ps but it can happen. PSA seemed to be putting out more than average during the panic buying and there were several documented instances. PSA made good in replacing them and it might be worth a call to S&W to see if they would consider swapping out the upper or barrel. Or, they might tell you that although you have to crank your windage, it may still be within spec. I don't recall off hand what the spec is for windage adjustment but there is a range. Either way, you have a great AR. Enjoy it!