There are many cold blue agents out there and I have had good luck with Brownell's Oxpho Blue. Go by the directions on the bottle. You will probably have to give the barrels more than one coat. You might get a decent blue but it will not be like a factory blue that had been rust blued. Hunter Arms barrels were a matte black finish when done not a shiny black like you see in most re-blued pictures.
Good luck and let us see with some pictures how you made out