Undoubtedly cast aluminum.
Al was a whole lot cheaper than brass at various times.
With the right additives it becomes very tough!
Along about the late 50's/early 60's aluminum casting went through a wild fad. There was tons of it left over from WW11. You can pretty much melt it on your kitchen stove in a saucepan.
Popular Mechanics and Popular Science were full of articles.
People were casting left and right all over the nation!
But then it was found that melting aluminum frequently, while not as bad as melting/casting quantities of lead, still, the health concerns are similar.
Occasionally, and in a small way, in hobby amounts, its fine.
You can get away with it easy. Cast an ashtray, etc? No problem.
But if you start playing with a lot of it, you are playing for keeps, so watch it.
yours Scott