It's all for fun anyway.... but the water displaces faster in a regular milk gallon jug.
A guy on another forum had tested the same ammo I had in the pic above. (45 acp Ranger). Anyway I got much less penetration than he did because my vinyl jugs didn't burst.
It's not a "my way is better" thing. It's just that you'll get different penetration results with a more stout jug. I don't know which one is more indicative of performance on a bad guy.