oldjarhead -
Actually, that is a [SA] marked holster for a 5" Lahti. It will fit a 5" Finnish Parabellum, but it was made for the Lahti.
The Finnish Parabellum that "redbear" bought has a 4" barrel that would, obviously, fit in the holster. The Finns did make a [SA] marked holster for the 4" Parabellum, as all of the original pistols had 4" barrels.
The picture below shows on the left a Finnish holster made for either the Lahti or the Parabellum and has the "half-moon" cutout in the mag pocket for the Luger magazine, while the picture on the right shows a holster for the 5" Lahti.
Luke