by I saw this YouTube video by Ron Spomer that he released just yesterday. He compares shooting water filled milk jugs with a .375 H&H and a .22-250 Ackley Improved. You have to watch the video to see which cartridge wins.
Shooting water filled milk jugs reminds me of my late teens when my friend Robert and I would go to the range and shoot them with everything from a .22 to a .30-06. The overfilled ones were the best as they reacted more violently when hit by the .30-06 bullet. Call it plinking or call it a penetration test, it just fun.
The overfilled jugs reacted more violently because of "hydrodynamic ram" because there is no ullage mitigating the shock waves ("ullage" the technical term for the void/air space in the top of the container). If you were to look at a projectile going into a stiff-sided container (e.g. a 23mm going into an aircraft fuel tank), you'd also see fluid shooting backwards out of the entry hole as the void created by entry collapses, creating a spurt. FWIW, I know this from doing aircraft vulnerability analysis at a defense contractor.
Scrappy is correct, water is essentially non-compressible. Not really surprised at the results either! 🙂