Rootsy, John is a first rate person to get the questions answered about the horn you might be looking for!..That said, everybody has their favorite way to carry their powder horn. I am right handed and carry my horn and bag on the right side, and if you think about it, that puts the powder horn, the farthest away from that fire and sparks from my flintlocks! This subject (right side or left), has been debated a gazillion times, but boils down to what you like to do!
Also, ..... and I repeat, Almost any cow horn can be rounded at the base, but I believe John is talking about the horn in general has a body that will not normally round. To many times, you see a horn that someone made that has a nice rounded base, but is over flared at the base, with the rest of the horn being oval or flat where it should be rounder!
I have rounded some natural oval bodied cow horns with heat and hot sand packing, but it is mainly more trouble than it's worth the time in doing! ... John just has too many nice horns to choose from!
Rick