Yes ,there were smoking tracers used in the BoB. I'm not talknig about 20mm cannons. Check out some original gun cam footages. It's perfectly modeled in BoB2:WoV by the way.

However, having to fiddle around in FMB to get the loadouts right - and not even then does it work - is unacceptable IMO. Whatever happened to the good old Il2 QMB?!

I did...
 

In the begining the Spitfire Mk I did only have "empty" loadout.
I did go to the "PLANE" menu and there selected the Group "RED".
Then the type of aircraft "FIGHTER".
Next in the left handside the Spitfire Mk I.
At the botom right side "LOADOUT".
This is the long part, you need to create for each gun, there are 8, a ammo belt there are 350 rounds per gun max.
Save this settings, this is important.
In the mission menu you have loaded you can change the load-out of every plane using the one you have created or the one provided by the game.

Have a nice game.

The hole weapons load out screen is just a mess, it needs a complete reworking
every time you go into planes menu, you have to select you plane, when it should remember what you was doing the last time you were in there, or there should be a save button in the planes menu, and not just in the weapons loadout screen.
And the load out screen just does not work, unless you use the FMB:confused:

Yeah, spit tracers are still invisible for me as well, default belting or custom.

For tracers do not put one or two but four of five near each other.

Its not that with a lot of us
The Weapons Loadouts, Just do not Work , unless you use the FMB