Added Gif to show sideways formation and travel of fireball from irl footage to additional information below.
When firing the main guns in tanks, you get no feeling of the violence of the blast.
The particle effect is also very much lacking, and more reminiscent of the black-powder charges used in the 50s to make tanks look like they were firing. A small flame at the muzzle, and a big white cloud.
It actually is a fast travelling, longitudal ball of flame that mushrooms out towards the front, with a quarter second stay time at the longest. From the front it looks like a vortex. Half a second after the blast, the barrel clearing device will blow the remaining smoke and powder out of the barrel, in the shape of a short, white puff of smoke.
Below are provided video references. {F21942}