This is a Urethane plastic casting of an original M38A2 Tank scope. (Originally used during the Second World War to find azimuth and sight M3 and M6 75mm guns mounted on Chaffee light and Sherman medium tanks.)
These light castings weight in at 3.1 oz. (The Original scope weights 13.8 oz!)
These are nearly identical to the illusive M38 Scopes used on the E-11 blasters carried by the Stormtroopers in ANH. If you want to make your Blaster look “Swarsy”, this is a sure fire way to do so!