by UnaStamus on Mon Mar 28, 2016 12:43 pm
Buying the cheap stuff from NC Star or UTG could potentially end in heartache since they have very poor quality control. There is a high probability of the sights being out of spec or really janky quality.
Take off your top handguard (if you have one) and lay the rifle upside down on a flat surface on the upper receiver. Make sure that the upper receiver is flat on the surface and then look at the front gas block rail. If the front gas block rail is also flat to the surface, you have a same-plane front gas block rail. If there is a gap, you do not have a same-plane gas block rail. There are sights for each separate application.
For metal sights, look into Midwest Industries, Troy or Magpul MBUS Pro.