I've shot a lot of water filled milk jugs, but I had my video camera filming them for later viewing. I also shot those 5 gallon plastic water filled cubes and compared a NP to an Interlock and filmed that one. Snow filled boxes caught some bullets, but as written before tied together phone books gave me a consistent media that I could compare one bullet to another in the same stack. Then number, note and save just the covers without all the paper mess. Back when I was shooting a .308 for my deer hunting, a big surprise was the difference in expansion in a Remington 180 grain round nose Core-Lokt vs. a 180 grain Pointed Core-Lokt through the same stack of phone books. That round nose was punching a thumb size hole out of the first book's cover and the pointed bullet took three to have a similar size exit. The round nose penetrated a couple of books less as well. Our deer camp never lost a deer hit anywhere with that Remington round nose Core-Lokt. Some years back Handloader ran an article of 180 grain .30 caliber expanded bullets. I contacted the author and ordered a poster showing all those bullets side by side. Of the 38 different bullets tested in 100 fps increments from 3100 down to 1400 fps three bullets each, that Remington round nose Core-Lokt was the only one on the entire poster that expanded with a nice mushroom shape, never lost its core at every velocity from 3100 down to 1400 fps.
Some of our agricultural deer shooters are missing what could be a real learning opportunity for lots of us. They could be photographing the exit wounds of deer shot with different bullets.
