Water isn't the greatest media to test bullet expansion in flesh. In leiu of 10 percent jello, one can use wet news print. What I've done, and haven't tried it yet, is shread news print and stuff milk jugs full. I figure to soak 'em over night before heading to the range. It'll allow multiple shots on the bottles and be easier to transport and less messy. I haven't had a chance to do it, yet, though.
I was going to test penetration of a .22 mini revolver against a hot loaded .22 caliber NAA super companion and maybe my .31 remmy against that. .38 is well documented. I've chronographed all my loads, .38, .45 Colt, .45ACP, 9x17, 9x18, 9x19, all my rifles, everything I own. I handload so a chronograph is a GREAT tool I didn't have prior to the early 80s when the Chrony, first of the really affordable chronographs, came out.
There is another penetration/expansion sight that gives more intuitive results because they use 10 percent ballistic gelatin.