I'm sure that is part of it. The round cylinder, as opposed to a square hammer seams to spread its side pressure out more evenly. And it doesn't slam back and forth or have much friction due to a close running fit, dissimilar metals, grease and the fact that a longer distance from top of hammer to pivot point on the tire give it less side to side motion. I wish I could take full credit but the idea came from a very smart friend of mine. When I was showing different power hammer designs to him, he looked at the hammers and said "That should be round". It's amazing how some folks have a gift.
At the risk of sounding prideful, I was thinking, since this concept of using a round hammer is not the standard way of hammer building, maybe this could be named the "Gobbler Forge Hammer Design" or some such. Lots of folks have their name attached to different designs of tools. Maybe this can be mine.
Gobbler