[IMG]http://i.imgur.com/X5NsG1o.gif[/IMG] Important is the size of the fireball and the distance it travels. Entire span of this gif in the video is less than a second: the staytime is very low. Ideally, the lightsource from the blast should travel with the fireball, instead of being static at the muzzle.
http://youtu.be/bZf3HkT-1XA?t=47s British Challenger MBT's. Note the complete absence of smoke apart from the puff being extracted from the muzzle and the large and -very- brief fireball. Also note the sharp, hard bang from the gun being fired.
http://youtu.be/2L8OTynmklw?t=4m47s
http://www.youtube.com/watch?v=Cm08yR-tyLM note that this is 18000 time slower. Note how the blast first expands outward (from the front it would look like a toroidal vortex) before rapidly moving right and out of the frame. The flame would then begin to dim at the back end at about the same time the forward front of the muzzle flash will have slowed down.
http://www.youtube.com/watch?v=zV0zti8tucU note the ball shaped blast being ripped forward, followed by the long smoketrail from the barrel being cleared after the shot. Further, note the vehicle rocking back after the shot and the barrel recoiling. At 30 seconds, you can see particularily well how the fireball forms and travels forwards.
http://www.youtube.com/watch?v=UH5KIbZUQps COMPARISON video of T-100 varsuk's firing in the update from 02.10. Especially compare to the first video of the challengers firing, as far as the muzzle flash is concerned.
http://www.youtube.com/watch?v=ey2IfVQNfVs Video of T-72s on exercise firing on the move. Shows how the relatively light tank works together with the bigger gun. Note the quickly travelling muzzleblast, and again, no large cloud of white smoke around the tank after firing.