Just like an unissued original, these are a tight fit when new so will need to be form-fitted to the pistol. You can dry fit it by leaving your pistol in the holster for a period of time, the M9 Pistol will require more time and effort to fit. You can also wet fit by oiling up your pistol and putting in a plastic bag to form fit.
Although initially designed for the .45 M1911 pistol, many service members have purchased them for use with the 9mm M9 pistol, but it does takes a little more effort to wet form this holster to an M9.