For a non-technical description of how a shotgun mic works, this summary by Hugh Robjohns (SOS) is reasonable: https://www.soundonsound.com/sound-a...tgun-mics-work

Obviously there are some variations on what is described there (e.g. two-capsule designs).

Yes, you can run into problems outside with reflective surfaces and, equally, indoors have none: for the latter, think especially of sound stages, where shotgun mics are very much at home.

And, yes, the reflective nature and the design of the mic will have an effect on the usefulness of a shotgun indoors. Also, having the mic mounted statically can reduce or, more worryingly (unless ignorance is bliss), reduce the awareness of any negative effects: when moving a shotgun mic around indoors (i.e. booming for dialogue) the problems usually become much more apparent.

For all these reasons, production sound recordists usually swap to a supercardioid or hypercardioid in reflective spaces indoors or outdoors, when their specific shotgun mic isn't suitable.

Cheers,

Roland