For roughing out or shaping large blocks of stone on the 8 foot tall 'big boulder wall' we are working on presently Gavin Rose suggested I purchase two special hammers for the job. Using this Bull Set is a 2-person operation - one person holds the hammer angled on its edge, set in place along the edge of the area of stone to be removed, angling the blade slightly toward the outside of the stone. The other person then hits it with the striking hammer. Gavin uses this method for shaping big stones back in Australia when he's building trails.
It's amazing how much meat you can take off a awkwardly round glacial rock using these hammers . With some precision angling and some fairly heavy swinging we have managed to get a lot of these large stones 'squarish' enough to fit much better next to each other in our jumbo wall.