Re:How to reload other player's revolver?
This is how it works. First all players draw a number of bullets equal to empty chambers in their cylinder. Then players who are supposed to load other players’ revolvers load them, in order of the initiative of the bullet (Gentlemen’s agreement).
So to answer your question. You take the bullet to your hand (spare bullets) and you load the other revolver (all empty chambers) from any bullets in your hand.
The general rule is that on a load you may always look at the bullet and on a swap you may not look at the bullet. Of course, if a swapped bullet ends up on a hand the owner of that may look at the bullet.