The MP15-22 has been one of the most fun guns I have ever owned. The issue may have been covered, but the rear site elevator knob simply would not turn despite multiple Hulk Hogan attacks & 3 broken hammers. Gunsmith says it's factory bad, & as I go to leave Gander Mtn. a salesman & I looked again at the 'detent' holes underneath the rotary knob. Next to that, was a tiny hole so small I reminisced about losing my innocence. So I ask for a paper clip, stick it in the tiny 'detent pin' hole and probed & prodded, (reminisced again)...& Viola'! Now it works perfectly through the full range of sight elevation. 
Anyone else have this minor but very frustrating issue???
