It went together fairly easy. I did notice the first time I assembled it that the barrel actually sat too far into the upper (make sense?) after I tightened the barrel nut down. How I noticed this was that when I installed the upper and lower receiver I couldn't slide them together all the way. I used some double sided tape strips to shim the barrel out so the hop-up would seat farther in. It was an easy fix and not a big deal at all. It is extremely solid.