from Steve's Militaria( Military Restorations):
I have been restoring antique firearms for years and have found nothing which will remove heavy rust from rifle bores as well as Evapo-Rust. I've gone back and re-done bores that I couldn't clean before, even with PB Blaster and a stainless brush & rod chucked into a drill...
I just plug the muzzle, stand the gun up, fill bore with Evapo-Rust and let set overnight. Next day I pour out the now black liquid and simply wipe out the bore, leaving a shiny coating. I like your product so much that I have added your link to my website, if you don't mind.