We have noticed that (by design) the Evo handguards can be sensitive to barrel nut torque; meaning that if you exceed 10ft*lbs of torque on the barrel nut the handguard itself can begin to deform in compression at the barrel nut interface. Note that the factory barrel nut is not tight with "high torque" but rather "thread locked". The intent is simply to hold the handguard in light compression against the upper receiver. Again, 10ft*lbs is the MOST that should be applied.
The factory pistol handguards seem less susceptible to sight elevation issues due to variance in barrel nut torque because the angle/1913 rail positions the front sight much further away from the barrel nut interface; versus the Sapper handguard where the sight is positioned directly over the barrel nut.
While we have been able to zero all of our test Evo's on factory iron sights without issue, with the variance possible in mating 3-4 large molded parts together like this... like they say anything is possible. We figured we would post a couple basic pictures here to attempt to show typical "squareness" of the Sapper handguards:
This geometry is very important, that the receiver be square to the top 1913 rail:
And of course that the 1913 rail is straight/parallel
The only potential issue that we can find (and maybe what @Rooftop Korean had done earlier in this thread) is that there can be some mold flashing left around this pocket: