I got to thinking about the 8# hammer. Sledge is not as precise a word as we may think. After a fruitless search of the internet, I picked up a 1950 Stanley tool catalog. The Stanley made hammer of this pattern is found under Stanley Atha heavy hammers and sledges, STRIKING AND DRILLING HAMMERS, and is labled "Nevada or Long Pattern. You could get them from 4 to16 pounds. Hand Drilling or Stone Cutters Hammers are a separate section on the same page. The next page lists Blacksmiths Sledges, in 8 to 20 pounds, and these have the full octagon faces like the engineer's hammer.
So, it could be a drilling hammer. I'd be willing to bet, though, that it was used by Oily's people for splitting firewood and banging things that needed heavy banging rather than drilling. It's the same kind my grandfather use for splitting wood.