Why bullet trails always lags 0.5 second behind bullet?
 

Whenever you fire a bullet or cannon shell, its trail doesn't show up until 0.5 second after the bullet going out of barrel.

Is this a bug or it should be like this?

I'd also like to ask a question to TD.

Since Cliffs of Dover is not as perfect as it was imagined, will you consider some more complicated enhancements of IL2 which you haven't think of before? For example, how about revamping some old and ugly cockpits (e.g. P47 and Bf109) in the game?

If you fire a bullet and pause the game you'll see that you're incorrect. It appears almost immediately following the bullet. What you're noticing is likely the fact that the smoke trail forms behind the bullet and then the plane catches up a split second later.

I think it also has to do with the location of the gun wrt the cpit. Wing tracers appear quicker than cowling/root tracers.
Maybe just a graphics thing...