The tracers in Cliffs of Dover are the most realistic I have seen in any simulation or game.
However, they do appear too "thick" (at close range) from the photos and vids I've seen.
Make them a little thinner and they will be perfect.
Here is a good film showing tracers. Start watching at 1:20.
http://www.youtube.com/watch?v=KFKT_...eature=related
Here is another good one from Germany.
http://www.youtube.com/watch?v=zgmDi...eature=related