Naval jelly is a whole lot more expensive and no more effective. I can get white vinegar for $0.99/gal and I use it for de-rusting tools and saw blades that I pick up at yard sales. Works extremely well but leaves a soft black film on the metal, easily removed by scrubbing with ScotchBrite or steel wool. The naval jelly is also so viscous that it may leave an air pocket at the pit and thus won't attack the rust. Keep the vinegar off the blue, and oil the barrel interior as soon as it's clean and dry. I'd flush with hot water after draining the vinegar, kind of like cleaning up after black powder loads.