TacFire's 308 dust cover seals the ejection port (which allows spent brass to exit the upper receiver after firing) from allowing contaminants such as sand, dirt or other debris from entering the mechanism.
Specifications:

Type	Dust Cover
Model	AR-10 Dust Cover
Dimensions	3.31" L x 0.88" H
Size	.308
Material	Steel
Action
Trigger
Safety
Thread Pattern
Finish	Black
Bolt Type
Hand
Hammer Type
Max Capacity