I have spun a revolver with one round in the cylinder. First, you wont wait for it to settle, so it doesn't matter. Second, a cylinder is pretty heavy, so even if you did, it's not that big an effect. Third, there is significant friction between the cylinder and the pin it rotates on, which will prevent it from settling in that manner. The 1:600 number isn't true.

Even if the 1/600 estimate(which I'm skeptical of) is correct, it wouldn't translate to that many people having played, but that many trigger pulls.

I think it's more likely that someone who plays once will play multiple times than it is for someone who has never played to start.