I continued to model the ordnance in the game and recently added the flak rounds and the bullets. The references I initially used was the WW2 flak cannons. The most widely used AA round was 22mm calibre, and thus I modelled the rounds based on this information. As it turns out, it's so small that it wasn't visible in the game at all. This is in contrast with the rocket and missile models which are to actual scale. Because those are launched from a position close to the player, they are visible when it matters. However as the player dodges and manoeuvres around, the flak rounds were almost never close enough to the player to see. My solution was to make them bigger. They ended up being almost 7 meters long in real world scale, and close to .5 meters diameter. This is massive. But to give the player the ability to see them, it was necessary. Similarly, the bullet rounds are the same, almost 7 meters in length.
Even after all this, I found that it looked crap. Previously I had simply drawn lines between the previous and the next positions. This had looked a lot better, and my conclusion was that it created the illusion of motion blur. I then adjusted my textures to blend some alpha towards the rear of the AA and bullet models, which did the trick! Additionally, with the use of models I'm able to make and apply illumination maps for the tracer rounds as well.
The bullet rounds are visible on it's way to the player here, and also some from the chopper being fired. With the models it looks much more realistic than the orange lines did. The design decision behind all this is to facilitate the shoot-em-up/dodge-em-up aspect of the game play. Instead of the bullets hitting almost instantaneously, it's instead very obvious to the plater that there's a burst of rounds coming his/her way, and the speed is balanced such that the player can react to it. Making the visual aspect of this work towards that goal is very important. Of course, there's no such thing as tracer flak rounds as far as I know, so those will not be visible at night and makes night-time engagement a bit more tricky.