Made from aircraft aluminum with a copper base.
Artillery Shell-WWII Theater Made Aluminum Ring. Which theater is the question? The fact that it is made of aluminum makes me think for WWII than earlier, but the driving band in copper goes to WWI Your call!. The shell is made separate from the three prongs holding it from each side. Finished with a copper driving band.
Simple design but a good deal of work went into making it.
From the Robert Borrell Artillery Collection.