I had this little clip on DVD, so I ripped it and thought I'd put it up here.
It's BoB era. A couple of seconds worth, then slowed down and repeated (badly edited too)
I've been laughed at in the past for suggesting that the on 8 x .303 mg variants the RAF tended to like to use Tracer rounds in only one gun (Tracer as in visible rounds) and then used incendiaries and ball in the others. The incendiaries being the early Buckingham type that left a smoke trail which was ejected from weep holes in the bullet (causing spiral tracer smoke).
I can only see 'visible' tracer coming from one gun (port side). That would be my only issue with the tracers in CoD, but the loadout's got every type of ammo used in the BoB RAF wise, so it's not really a problem.
I think I remember Oleg saying that the human eye sees tracer length at about the same length as a video camera running at 92 fps would. I could have dreamt it though.