I'm assuming you mean, like your shotguns ... to mean you strip them down and clean them .....bfore you oil or lube them. Rem Oil is a good oil, but so is Break Free, Rem Oil, Wilson's lube, etc.
Cleaning is different than lubing / but I presume you know that ..... and what you use to clean them is mostly a personal choice ( Pro 7, Hoppes, Barnes, etc ) but you need to get the frames, slides, barrels, etc cleaned and lead or copper removed as well. After they are cleaned, personally I alwasy lube the slide, frame, springs, bushings, etc for re-asseblly with a light out - and Rem Oil is a good product - although I prefer Break Free especially on the slide. Internally on a shotgun like the trigger group on most sem-autos or on an over under - I will use a light spray oil - and again Rem Oil is fine although personally I use Rig Oil.