JHP's fully expand within 2" or less of penetration normally, at handgun velocities.
What occurs is that the exit on the milk-jugs in the front of the stack is larger because there is more velocity at impact, thus there is less stretching and more tearing. Think about a piece of paper shot with a .45 vs one shot with a .223. The .223 holes are cleaner, and larger in diameter compared with the projectile that made them.
First, I am not doubting you. What made this different is that the exit hole and entrance hole into the second jug were just that, holes. Not the stretch tear that I have seen with GD's. I understand that most JHP expand in the first 3". However, I do not follow your analogy. When I shoot a 45 through paper I get at 45 hole and when I shoot a .223 I get a .224 hole. Even went back to saved targets of both calibers and measured. Also, following your thinking why would the entrance hole on the first jug be a perfect round hole and not a stretch tear. The reason I brought it up is because it was different than other bullets. Whether it was a velocity induced stretch tear I do not know, but it was the only bullet that tore a chunk out of the jugs that was larger than the exit hole on the second jug and the entrance and exit on the third.