Dust Cover Gas Blowback Rifle (GBBR)- This small flap of metal is used to keep dust and debris out of the bolt/chamber area when the rifle is in transport or not actively firing in order to increase the reliability.
I received something other than what I ordered and paid for. Instead of the Sotac Micro 3x, I received a Swamp Deer G43. The promise to return the difference has not been fulfilled so far.