I've tried three or four times to kill Saturn, but he has too much health. I've used all manner of weapons, but I run out of ammo every time. I haven't tried multiplayer, but I don't think that will work much better. Does he have a weak spot or a crit spot that I couldn't find, or a special type of weapon that does extra damage?
Saturn's guns are destructible, which means that you can reduce the amount of firepower being thrown at you. They can also be used to trigger Second Wind.
It's resistant to Explosions and to Slag (but can be affected by the Slag De-buff that amplifies other kinds of damage). It has no weak points.
Finally, using cover is a great way to survive this encounter as Saturn can't realistically hit you through walls or other types of barriers (thus allowing you to survive for longer).
This encounter is all about minimizing the damage you receive while dishing out your own damage. Avoid using explosive rounds and keep your shield up at all times. If it shoots rockets, take a moment to see where they're heading, clear out of that area and you have a few seconds to dish out damage without an issue. Finally, don't forget to use your Character's Ability.
Keep your eyes open for the possible spawn of a Pup-Skag, as killing this creature may also be used to gain Second Wind.