I have used it for the last 40 years for gun flush, bore cleaning, lube and anti rust. I keep a sheepskin with it in the gunshop. I used it exclusively for years as a wipe down, rust preventer. I get better performance now with G96. G96 leaves behind a silicone film that works better on bluing to keep the rust down but G96 is a poor penetrant and flush/cleaner.

If you don't want to carry around and use but one product for all your gun cleaning, wiping, anti-rust jobs, WD40 is it.

Here is how I rate it for guns:

Anti-rust: very good (Was excellent before I met Mr. G96)
Flushing: excellent
Bore Cleaning: good
Lubrication: fair
Penetrating/Breakfree: excellent