The 18th C musket/flintlock was cleaned with water and a rag. 

When possible, it was hot water to resolve the residual powder, which was corrosive to the metal barrel and lock. Tow( remnants of fibers from making cloth) and rag were used for cleaning. 

The British polished the metal and furniture ( Brass) with Brick Dust and Sweet Oil. 

Brick dust is what you think is the pulverized dust of an English brick mixed with Sweet Oil ( olive oil) to make an 18th-century metal polish.