Odd YHM flip-up sight fitment on Bushmaster barrel

I'm helping my cousin install a YHM flip-up gas block on his Bushmaster, and it would appear there is a slight fitment issue. When installed, the YHM sight/gas block does not completely cover the unfinished sections of the barrel where the old FSB was previously mounted.



Installing the sight without the handguard cap improves things ever so slightly, but it is still an issue... not that doing so is an option for this particular rifle anyway.

So is this a common occurrence for these YHM sights? Or perhaps Bushmaster barrels are to blame? Anything we might be doing wrong? Can it be corrected or is it just a size difference between this sight vs. the original FSB that my cousin will just have to live with? :banghead:

Yeah, I just got out the calipers and did some measuring of the original FSB and the YHM sight. Their dimensions are definitely very different, so it makes sense now, wish I thought of that sooner. Guess it's time to test fire and see if the gas port is lined up...