Muriatic acid, is hydrocloric acid. Hydrocloric acid can cause hydrogen embrittlement, not a good thing for your steel parts. Use the phosphoric acid or use a viberator bowl tumbler. The kind that ammo reloaders use to clean their brass. Harbor Freight carries different medias for cleaning. One is just for such a process.
Home Depot has a metal prep. that is phospuric acid based. I think the brand name is Strip-ease. $13-14 a gallon. It is in the paint section. I have used it to clean small parts. Just soak for about 30 mins for surface rust and rinse with water. My parts came out looking like new.
