This photo shows the BCX52-16's Collector waveform in a Buck converter with 5v input at 160ma draw.
The Base current is now 20ma.
The choke is 50uh powdered iron running well into continuous current mode.
See how the transitions now look faster compared to when the load was resistive.
This is deceptive, there are actually hidden losses. The transistor will still be passing some of the tail current caused by the Storage delay after full voltage has developed across C-E. This is a common cause of loss when BJTs are switching inductive loads at high voltages.
In this case, because the voltages involved are low, the losses aren't that much.
When I put the Schottky diode between C-B, the efficiency drops from 78% to 67%.
Extra: The transistor also still has the sluggish turn on although it's now not visible. What's actually happening is because the inductor current is keeping the flywheel diode in conduction, the voltage stays clamped at near 0v until the rising transistor current matches the inductor current at which point the voltage suddenly rises.