What a tracer should look like (before spazzing just look).

[II./JG1_Wilcke]

To get an idea of what were dealing with just take a look at a .303, .50 and a 20mm aviation type round, look at the base of the projectile and you will see the area available to setup the tracing material. Its pretty small in diameter. So that will give you a rough approximation of how 'thick' the tracing should be in game.

As for the 20mm cannon ammo, yes the barrels were rifled. Oh and projectiles do not fly in a straight line the definitely follow a curved flight path affected by ballistics and gravity. Bullet design, along with muzzle velocity also affect how flat the barrel will shoot; but there is always an arc that intersects the line of sight twice.

The military folks and hobbyists that have fired a variety of tracing ammo through various automatic weapons will know what we are talking about here.