To have a longer gas tube, the gas block needs to be further forward, so the gas hole in the barrel would need to be further forward, so you'd have to plug and drill the barrel.
BTW - I also have the S&W M&P 15 OR. I put the Magpul MBUS on it before I saw the waring about them "melting". I have only 600 rounds so far, without issue. That includes once dumping 4 30 round mags as quick as I could (end of first time out with it). It got hot enough to smoke all the oil off the barrel (it was impressive
), the front sight was very grey, and being sure it was toast, I thought, "guess I deserved that, sorry little MBUS"
. But it cleaned up fine, and keeps working prefect. I like the Magpul MBUS a lot, we have them on our M&P15-22 also. But to not have to worry about the heat issue, and to get just a little solid bottom rail, I'm changing the standard gas block out to the Yankee Hill Hooded folding sight/gas block with bottom rail this weekend:
Flip Front Sight Towers With Bottom Rails
I want the lower rail to put a bi-pod on from time to time, and a light/laser at other times. I have the Magpul hand guard (carbine length=short) and like it a lot, and want to keep all of it's space for my hands, not hanging stuff off of
.
That's one of the things that makes these AR so much fun, there are so many options and different ways to configure them. That's also what makes it confusing at times.
If your not set on the Magpul MBUS, there are many other folding front sights that fit the std rail height. Many less for the "gas block rail height". They each have their advantages.