I always leveled my gun, at that level, where there are several Undead Raiders. They can give the same points as bosses but they take less time. El Sudoron is good, just inside the entrance there are always 2 raiders.. I shoot them when they are far enough away to come to a stop but close enough to get them to draw their swords. That way, you don't need a healer.
And I always use lead shot and hit them with at least 6 steel shots (sometimes more or less...experiment). They do very little damage but they always help to max the score to 115. I also find it easier to do it alone so I don't have to share the rep.
When you gun gets higher you can switch to Kelpbrains. They act just like Raiders. Just remember to use at least 6 SILVER shots on the Kelps instead of Steel.
Might not be the perfect solution but it works for me...
