Roughly ranged my L85 today by shooting a mate and getting him to walk away from me incrementally. Then we swapped and he shot me.
We measured my stride as being about .65m, meaning roughly 15 steps equates to about 10m. So what we roughly guessed as being 55ish metres is just about the point where it took too many shots to hit someone for it to really be a viable target during a skirmish. Though shots were still flying past me at 60m, just not hitting because of horizontal drift and the hop having too many negative effects on the BB's flight pattern.
I've added my vote in the 50-60m section.