crystal math

maybe you fired weapons and hit nothing? I don't ever remember zero being displayed

Good point.

But wouldn't that lower my overall accuracy well under 39%?

maybe the weapons are weighted by the (amount of shots)/(max_no_shots_per_second) or something like that.

That cannot be answered with the information that you provide.

No, why? Let's say you've fired 100 LG cells hitting 40 and then shot two nades which didn't connect. That makes 40 hits of 102 shots (hence 39% accuracy), but the 0% for nades will be hidden as "--".