
The model M is the larger of two 9 mm Largo variants of the A/B series of 1911-inspired pistols that led Star design for the next 60 years. The models A, B, P and M had roughly comparable upates over the years.
The model M pistol is essentially the size of the slightly larger model P, and presumably is designed for longer service life or everyday use of heavier loads. Some histories imply this was the original design size, and the A/B size is reduced from this but I have no way to tell.
Download a manual for your model M-series pistol.