The upper receiver is the top part of the AR-15 platform, which houses the barrel, bolt carrier group, and other components.
M4E1 upper receivers from Aero Precision often feature a one-piece design for increased rigidity and strength.
Barrel :
The barrel is chambered in 5.56mm NATO, a standard caliber for AR-15 rifles.
Length and profile can vary based on the specific model and user preferences.
Handguard :
The upper may come with a handguard (or rail) for accessory attachment.
Aero Precision's M4E1 uppers often feature their proprietary Enhanced Series Handguard.
Muzzle Device :
Some complete uppers come with a muzzle device, such as a flash hider or muzzle brake.
Forward Assist and Dust Cover :
An M4E1 upper typically includes a forward assist and a dust cover.
Charging Handle :
Some complete uppers come with a charging handle, while others may require you to purchase one separately.
No BCG (Bolt Carrier Group) :
"Complete" in this context usually means that the upper comes fully assembled but may not include a bolt carrier group. The BCG may need to be purchased separately.
