just looking at pictures it's a little deceiving. the socket is for sure 3 inches long. it doesn't look like it in picture but i've measured it a couple times and without a doubt it's 3 inches long. it's like 3/4 inch inside to inside diameter for socket as well. it really kind of looks like this one in my opinion but you can't see the marking..
Looks like a Russian M1891 socket bayonet. Those were used all the way up to WWII and there are tons of them around in many variations and manufacturers. Check the position of the manufacturing stamp in your picture and the link above...