ANTI AIRCRAFT SIGHT

Here is something that I have had for at least 40+ years. I used it in displays and showed it to everyone trying to figure what gun it went to and from what country. It is 10 1l8” wide and 12 3’4” tall with the mounting bracket. I would presume that it would be on a larger caliber than a machine gun. Something at least 20MM but I believe it came from a much heavier 37MM, 40MM, 0r 5” cannon. If anyone knows what weapon it came from I would be interested to finally find out. It has been used and saw some hard usage, the black paint has some rust coming thru. The circular pattern is not nice and flat but has a lot of character from hard use. Condition good