This is my Gun Blair Build. Allround Setup for all content.
Keep up max stacks of your buffs from 1st (6x) and 2nd skill.
Depending on how how much targets the spread hit, that amount of buffs you will recive from 1st.
Regardles i recommend going for 3x 1st skill. always use your stacks.
Use 4th when Bosses spawning.
Modifier is very important here for Ancestor Mod.
Prio Stats
skill critical hit damage
dimension skill modifier
dimension boost ratio
harmless negative like MP
Focus on using Beam Rifles and add high Fire Rate on them for single target dps
Kings Guard Lance works also quite well on him.
Otional Changes:
If you like, change vs Boss Content more to Duration and if you like also hyperfocus.