View attachment 1890465this is called a "bullet end" the tip is cut off once the work is being trimmed out with fixtures such as cut off valves for sink supply lines...1/2" copper plumbing. It allows the system to be pressure tested prior to trim out. The bullet like tip is discarded and the threaded fitting or what ever else, is soldered onto the end of the pipe where the bullet end was.
I really hoped it was some ancient copper thingie that had never been seen before...there still is the mystery of why it was at the lake? perhaps some carpenter put it in a 3/4" pipe and put his air hose on it and shot it out like a bullet!