What caliber is the old mars pistol?

The Mars Automatic Pistol is was available in a variety of 8.5 mm, 9 mm and .45 calibers. These were all bottle shaped cartridges with a heavy powder loading, making the .45 version the most powerful handgun in the world for a time (very early 1900s). Therefore, I would suggest the .45 was a special load manufactured by Mars and not you standard .45 acp.