It rolls, deforms and fragments inside the body.
We only sort of disagree on this one. As mentioned earlier, those impressive wounds are caused by fragmentation... and when it's fragmenting, it's not really "tumbling" anymore. If it were, it'd just be getting deformed, not fragmented.
Ex: A 5.56 (or 5.45 I suppose), when working as it's designed (well, technically, NOT working properly.. wink wink), is only tumbling in the same way that a glass jar is still "tumbling" when you throw it at the ground and it shatters.
I don't have sound at the computer I'm at, but nothing in those videos showed much in the way of proof of tumbling. I've seen similar-looking gel tests with handgun rounds. It all depends on the variables, which are pretty much never listed on YouTube (i.e., 10% Mold, 15%, whatever).
Of course, that being said, a rifle is a rifle and a pistol is a pistol, to quote Old Painless (not related to Fallout).
And I suppose I should refine my position on tumbling a bit by adding "in general." There are a billion ways a bullet can react when entering tissue, but in general, it's not going to buzz-saw through flesh.