I went back to this guys garage/estate sale and he said it was a bung hammer. A little worried putting that phrase into a google search
. Well there are bung hammers for sealing and unsealing beer barrels. Looking a little further you guys are correct it is a dead blow hammer just lost it nubbins. This is a Craftsman hammer, this guy had a lot of good old Craftsman tools.
Knowledge on this site here is great