i also use a .54 cal bore brush in my .50cal.you almost cant tell difference.as for crud, for 35 years ,i very seldom ever used a bore brush in my hawkins .50cal.i always cleaned gun with warm water/soap after shooting it. i think thats the reason i neve, to my knowledge had any build up.i still use bore butter with rb and on my patchs.makes seating ball a lot easier.i dont use it for storage even tho i never had rust all those 35 years.this is truth from a hunter that is out in all kinds of weather.