the merger of remington and union metallic cartridge was in 1912.
Where there's one, there are possibly many...
The gunners should not have a difficult time dating it's production run.
Your particular headstamp is a style that went out of use in the mid to late 1930's. Here is a link to the style that replaced it. The replacement went into use by at least the late 1930's. I am sorry that I don't have an exact date on that for you.