No you can't shoot 9 Mak (9x18) in a .380 (9x17), because its 1mm longer and won't fit. I've *heard* of people shooting .380 in a 9mm Luger (9x19), just as I've *heard* of people shooting .40 in a 10mm, but it's definitely not recommended. Pistol cartridges such as these headspace at the neck, so the only thing holding a shorter cartridge in a longer chamber would be the extractor, which is always the weakest link in a pistol.
I think you can only shoot different cartridges in one gun safely with revolvers, such as .38 in a .357, .44 Special in a .44 Mag (but not vice versa), because they are held in place by their rims, regardless of length.