On pic you posted, it that a beater rod, or part of the cleaning rod sticking out of receiver?
If cleaning rod, clamp in a vice and get western about pulling (not twisting) and jerking straight out on the barrel, with another person helping to pull & jerk.
May have missed it, but are brush bristles wire or nylon? Sometimes on the twisted wire bristle holding type, the danm end will break off and jam the rod in beside it, so pulling is better than driving it further in. The twisted wire for holding brush bristles can be steel, and beating on it with a softer drift can still cause the harder wire to mar the bore.