Why is it that both Cybertron mode Megatron toys are mistranformed in each and every picture I can find?
The gunbarrel is supposed to be on the front facing forward, not on top facing backwards. It's like that in the cartoon:
Click to view attachment
As you can see the back-end of the gun is also facing forward as a cockpit, meaning you have to fold up the gun to make that work.
Both toys show that the barrel can indeed be flipped (and I'm guessing rotated around in case of the deluxe, since the flipping joint is on the top). Heck, the Voyager even has a hexagon-shaped hole in the front of the ship to fit it in nice and snugly: http://886.cn/4RBUQ6ek3