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. Mfg: Sinclair International