Star, I don't know what the MS model is. Could you explain or post a picture?
The MS is just a full size model, in the line of the model A, but way more robust, it is about the same size but 3 mimimeters ticker, with a weight of 1115 gr. unloaded. This allows the pistol to take calibers as the .45, in fact is the same pistol as a PS. It's the largest frame on classic models.
The first run of MS was produced in the 60's, and made in 9 Largo, it was a "heavy" Largo pistol. The second run, was produced in 1987, just 425 produced acording to Antaris, all in the 9 Parabellum caliber, and a few of them were sold as multicaliber sets that included a complete .45 upper. They were fitted with 30M sights.
Fewer examples were sold also in .38 Super Auto.
Here is my MS, with the .45 caliber mounted, hope you will like it: