How do rimless chamberings work in single action revolvers, 50ae in a BFR or FA, or say a Bisley or FA with a 45ACP cylinder?

They headspace on the mouth of the case.

If the brass is too short, or the crimp too heavy, or the cylinder demensions not just right, sometimes the round will not fire.

I have shot a S&W revolver in 45ACP quite a bit.

The advantage with it is that you can and should use moon clips.