I use hotwater with dishwashing detergent as they are the best known productsfor getting something squeaky clean...and a hot water rinse to rinse off the dirty salty solution.

The reason I choose to do this is because I use bore butter lube and want no buildup in the bore what-so-ever...and my decisionto usesteaming hot water can best be described with this analogy of bore butter on the walls of a bore, to egg residue on a breakfastplate:

If you hold a breakfast plate under a cold water faucet to rinse of the egg residue, it sits right there clingling to the plate for ever;
But if you hold it under a steaming hot water faucet, the egg residue melts and slides completely off the plate, add a drop of dishwashing detergent and the plate issqueaky clean.

If it's not 100% removed after each use...100%...there will be leftover material which is the beginning of 'buildup'...and at some point buildup willaffect accuracy and/or trap moisture or contamination in the bore which will lead to rust or corrosion...so I take my barrels back to the bare raw metal after each use, and use steaming hot soapy water to do so.....my .02 cents.