Nitriding would be my choice, and is on most of my products. We use a salt bath nitride, mostly on 4140 steel, and have not noticed any deformation after the process. It is a relatively inexpensive process if you can fill a minimum batch and provides a subsurface hardened layer, rather than a coating.
Chrome lining has it's advantages, but I think that most nitrided barrels will hold up well to continued use.
Chrome lining has it's advantages, but I think that most nitrided barrels will hold up well to continued use.