Did you lay the round on something for the 105? Like did the breech slide open horizontally? The 120 has a breech block that slides up and down.
The 120 round casing is combustible except for the very last 3 inches (aft cap) or so that got ejected into the turret. Obviously red hot aft caps contacting a combustible 120mm tank shell didnt turn out well for the crew so they were stored behind balistic doors. Before a round was fired the door had to be closed which axed the practice of lap loading. The door was hydraulically controlled by a knee switch and took about 4 seconds to open fully. You could grab a round in the sweet spot after about 1 second though. I'd have loved to see this vacuum loading!
As for the vacuum in a turret I've seen what sabot rounds going a mile a second do to people inside a turret. Sucks em right out that 3 inch hole. Well most of them anyway...