Vintage Banjo Oiler for Military Firearms

Description

This was my late husband's Banjo Oiler which I know nothing about.  We have had it hanging on our wall for years.
I assume it is brass or copper - not really sure.  It is vintage and fairly heavy.   It is 5 inches in length and the round part is 2-3/4 inches.
Thank you,
Doris Fulton