A pulsed detonation gun, according to one embodiment, has a first section (19, 20) into which a detonable mixture is injected and a second section (21) into which a coating precursor is injected. A detonable or reactive mixture is formed and ignited in the first section (19, 20), and the detonation or reaction products expand through the first section (19, 20) and into the second section (21) into contact with the coating precursor. Detonation products containing the coating precursor are discharged through an outlet and contacted with a substrate (25) to produce a coating. The device is particularly useful for coating the inside surfaces of small-diameter tubes and a variety of other difficult-to-reach substrate surfaces.