1916, a .455 Hand Ejector, Second model.
These were made for British (an allies) for WW1. Many came back to US as imports, etc. They are often modified to shoot 45 ACP and sometines 45 Colt.
I have seen a number of these also significantly modified with adj sights, shortened barrels, etc.. often confused with 1917 US model
These are ones i have been a caretaker of - original ones, still chambered in .455.. I actually sold one a while back, but still have two in the safe..