That looks like it could be part of a powered bucking system.
Whats a bucking system?
Did connect air to it, and does something but I have no rivets of the size to try
Comparing the 1/4 gun of today
Which is a one hander, this one takes 2 hands and has an upper handle. I'll figure this out one of these days. Who knows, it may just be really old and they now can make them small and light weight
Well, AD - You can always say your's is bigger! LOL