Hello Rick, Very nice brass bladed dagger. Can you tell me if the collar is one piece or if it has a solder seam? The earlier ones that I have seen and handled seem to have seamed collars where the later ones usually have solid collars which were most likely made from spent cartridge casings. I have heard that these brass and copper bladed daggers are believed (when used) to be able to inflict a wound that will not readily heal making them more prone to infection thus leading to the subsequent demise of the victim. I have one in my personal collection with a copper blade that is coated with arsenic.
Looking at your dagger I would date it to the first quarter of the twentieth century.
Best,
Robert