I'm gonna go waaaayyyyy out on a limb here and say it is very possibly a "blank" fishing lure. Have you tried to see if it will float?
The reason I say this is I once was an antique fishing lure collector and have bought many old tackle boxes filled with stuff from
estate sales. A couple of these boxes co
ntained "many" blanks where the fisherman could design his own lure. That would account
for the brass coating. Some lures are made a little on the heavy side so they will sink when pulled by fisherman through the water.
Others were made to float on top such as a popping bug. The line around it resembles where they would paint the head and then
"scale paint" the body. In those boxes were the eyelets with the screw threads for tying your line to. I have never found one myself
while detecting but if it hit like a dime or quarter it is probably a soft lead. I have a book on these things too and there are blanks
in there that are valuable in good condition and without holding it in my hand, that's what I would say it is as it is the exact shape
of some of those blanks.