1. equip revolver to hands
2. Press gun spin key Ex:F10
3. Player raises revolver with right hand and spins the cylinder once with their left hand, rotating it an unknown amount of times but not always the same amount of rotations. Ex: anytime it is spun it could be anywhere from 1-4 full cylinder rotations as that way it will always be random where the bullet ends up.
4. To return revolver to the original state that guarantees a shot with a trigger pull, simply unload it and reload.

The ability to do the animation over and over again would be really cool but it is not a priority

If you want to really put your animation guys to work additional animations for the character putting a gun to their head (like under their mouth or a faster default animation) would compliment this addition by making Russian roulette not look so repetitive when there are multiple people playing at once but it is absolutely not needed at all.