The action and carrier key passage on AR rifles are areas which need frequent attention to maintain top accuracy. Our AR-15 Action Brush does an excellent job of cleaning the powder/carbon blowback from inside the receiver body.
The carrier key passage needs to be cleaned out with a stiff stainless brush to maintain proper functioning of the rifle. Both of these brushes are sized correctly for their specific purposes. All AR cleaning kits should include both brushes.
Sinclair, Issue:5B, Page:158