In my very first pistol shooting match, one of the RO's asked what my loads were - he claimed to see my bullets travelling in broad daylight. The loads were quite light because I had only started reloading. If memory serves correct it was 135gr LCN with a middle-of-the-batch load of powder.
When shooting with a spotlight at night, the light reflected back from the base of a flat-based bullet, can often be seen with the naked eye. Much like a tracer bullet.
I have also observed light reflected off the base of a handgun bullet, when shooting with the sun behind you. You won't easily see your own bullets, but an RO or SO standing beside you can see it.