Hitting High: Pic Gasblock w/ MBUS Front & Rear

AR/M4 AR Technical Discussion
1

I’ve already searched so if I overlooked something please direct me to it.

I have an S&W M&P15 OR with MBUS front and rear and am impacting approx. 3moa high. The top of the front sight post is practically even with the protective wings with plenty of thread visible below. Any suggestions or sight options available without changing the gasblock out or having the sight post above the wings?

Thanks,
Keith

UPDATE: This carbine has the gas block rail and the upper receiver rail on the same plane. I got the it zeroed at 100y with 5.56 55g ball ammo using the ghost ring. Switching to the small aperture has me approx. 2.5" high at the same distance. Heat concerns duly noted. Thanks for the advice gentlemen.

2

It almost sounds like you got a higher gas block height MBUS instead of a regular one. You might measure it against a known good regular one to check.

3

You mean lower?

4

Yea, I guess I do at that. Thing is, the photos I’ve seen of the OR show a railed gas block even with the receiver rail instead of a railed handguard.

So it would seem that either the MBUS or the gas block rail are the wrong height, yes?

5

Pictures would help greatly… The BUIS or the GB would surely cause the issue…

6

I think there is only one height of MBUS made. Where did you get it? There are a lot of fakes out there. I’m also pretty sure the MBUS is not meant to be put on a gas block due to the heat.

7

TF82 nailed it,…there is not a MBUS model sight that is the proper height to be gas block rail mounted.

8

BOOM. +1

Also GB rails are LOWER than the pic rail on a std flat top.

9

You know, that’s what I thought too, but briefly looking online you seem to find mixed answers for the M&P optics ready. It seems to me that that must be the case here though, or a fake MBUS. Either way, the MBUS isn’t meant to sustain the gas block heat.

10

Not on the M&P-15 “Optics Ready”, the gas block is same-plane as the receiver rail. (At least it was on the one I owned.)
This throws a lot of people off: it is a gas-block but it is tall enough it doesn’t take a “gas block height” front sight. Maybe they make a new version now but just recounting the one I owned; I used “same plane” front sight for it. Metal (fixed) front sight, plus a MBUS rear sight is what I used.