I've never seen ball ammo that doesn't fragment.
That's what it's designed to do.
Past 400m, velocity begins to drop off quickly and that's the key to fragmentation. Perhaps the dense phone book material kept the bullet from splitting. My XM193 will detonate in water.
Wow. I've recovered .30-06 ball, lots of it, that has remained intact after firing into wood or sand. Same thing with .223. I've never seen them fragment, unless you hit a rock with it. Incidentally, shooting at water is almost like shooting at a rock (at rifle velocities). I'm not surprised that the ball fragments under those conditions.
Soaking wet phone books are a poor man's ballistic gel, BTW. It moves out of the way of a bullet quite nicely, and leaves a well defined wound channel behind. I've used them to test .44, .38, .357, .223, etc. Ball never breaks up. Ever. Hollow point pistol bullets expand nicely in that medium, and even they don't break up (unless I'm using the wrong bullet for the velocity - like bullets designed for 850fps moving at 1,400 - then they come unglued).