Because of the high serial number (400K+) I'm going to assume it has an exposed hammer????
It's a 3rd Model "AUTOMATIC EJECTING", no patent dates, with MASS. (abreviated) it's a 3rd Variation made sometime in the 1913 to 1915 time frame.
Nickel plated, with 3 1/4" barrel and black hard rubber, "Target Logo" grip panels makes it the "standard" issue. It was made to handle smokeless powder loaded .32 S&W or .32 S&W Long FACTORY loaded cartridges.
Here's a pic of what your's should look like, except this one has a blued finish: