One piece upper - Aero Precision M4E1 Enhanced 16in .300 Blackout Quantum Handguard Complete Upper Receiver with Flash Hider

One piece upper receiver only fits an Aero handguard. I have large hands but this handguard is huge. It's as fat as a quad rail and isn't This one returnable. The top front of the handguard has a 5 slot proprietary pic section that is screwed into the handguard. What a dumb design. Although there are M-MOK slots they start too close to the fixed section which prevents mounting a pic section abutting the front without modification. Real estate is precious on a short handguard. I have purchased a lot of Aero parts in the past but this design has turned me off to their stuff.