OP most gun lubes are just as good as any other. Motor oil is for motors. Gun oil is for guns. (If someone wants to fight me on that saying "oil is oil" go fry an omelet in WD40 and lemme know how it tastes.)
WD 40 is really not an oil. The WD stands for water displacing or displacement. It is really meant as a rust preventative, and is ok for very light uses such as a squeaky hinge.
I have been using Mobil 1 15w50 for years with good results. a little stays in place. Motor oil is excellent for rapidly sliding surfaces, think reciprocating pistons, and fast rotating surfaces as bearings, both of which move at must faster speeds than any firearms slide or pivot point. If it can hold up for hours and hours at temperatures most firearms will never reach I don't see why some folks say it is not good for firearms lubrication, after all it is a "LUBRICATING" oil.