Yeah, the bullets were heavy solids. Bell eventually went back to the 7x57 not because of its slightly heavier bullets, but because the cases for Austrian 6.5x54 ammo split too often on firing. Otherwise he would have stayed with the ".256," because his customized rifle was very light and handy. Bell did sometimes use a .318, which he preferred for more difficult angles on brain shots.
No doubt some elephants were taken with the 6.5x55 using solids too, but I can't recall reading about it.
“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.” John Steinbeck
