For most of us, chambers and forcing cones can be adequately cleaned with the same brass brush we use to clean the bores, especially if the area has no pitting or rough tool marks. When I acquire an old vintage double that has really dirty chambers/forcing cones with an accumulation of powder residue and plastic or lead fowling, I might wrap a little 00 steel wool around an old brass brush to increase the diameter and make it a bit more aggressive. Most any bore solvent will do, but Hoppes No. 9 still smells the best... especially the older stuff that contains nitrobenzene. Spinning it on a short rod chucked in a hand drill makes it quick and easy.
