Transistor as switch
From your question, you've only shown 2 data points for your BC546B transistor.  If you look at the datasheet, here are the electrical characteristics, specifically the base-emitter on voltage



So the minimum is 0.55, and the maximum is 0.7 to 0.77. The manufacturer's datasheet guarantees your transistor will be somewhere within that range.  

Right now, you've only shown us 0.5V and 0.6V for Vbe.

I'd also recommend measuring the base current, Ib.