CENSECFOR M16A3/M4A1 Service Rifle Practice Test 2026 – Full Exam Prep

The ejection port cover and the housing for the bolt carrier key are part of the upper receiver assembly. The ejection port cover sits on the upper receiver’s ejection port to seal it when not cycling, and it opens as the bolt and bolt carrier cycle to eject a spent cartridge. The bolt carrier key is mounted on the bolt carrier and is housed and guided within the upper receiver as the bolt carrier group operates. These components are located on the upper half of the rifle and interact with parts of the upper receiver, not the lower receiver, magazine group, or buttstock. Therefore, they belong to the upper receiver assembly.