This upper fit perfectly with my m4e1 aero lower. It is a quality upper, built well and will last many years to come. Thanks grid for a great product
*****Ammunition Notification***** Ghost Firearms test fires every custom upper to verify cycling. We do not guarantee cycling with all ammunition due to vast differences in the quality of ammunition. We will only warranty cycling with US made ammunition. We will not warranty cycling with imported, steel cased or reloaded rounds.
Please allow adequate time to build and test fire all uppers