I find the lack of common sense disturbing...

Personally, I like the way the tank looks right now. If I had to change anything, I would first have the bulge in the middle of the barrel made a little bit larger all around. The next thing I'd to is give the tank some kind of muzzle break, because I've never seen a modern tank without one. After that, there isn't much else to do without making it very un-Halo.