What's this fascination with pistol calibers in revolvers? Why have to mess around with moon clips, and such.
If you want to carry a .40 buy a semi in .40. You want a .40 backup gun, get another of the same, talk about ammo compatability, we're talking mag exchange.
Then there is the capacity to consider. 5v15 or so. A loaded gun and a spare mag and you have 30+ rounds, without having to carry 5 extra loaded moon clips.
But then variety is the spice of life.
The above was written in a semi serious, semi humorous vein and is not intended to start any flame wars, but in the hope that maybe you can help me understand this desire.
If you want one just because it would be neat, cool. If you want one because it would be a good ccw, I don't see the point.