This is the build I'm using for Wave of Light. It's probably not the best.
I did not expand the magazine size. The unique ability procs on reload, so it's more advantageous to frequently reload. Instead of expanding the magazine size, I used Reload Focus to make reloads faster and get a smidge more Critical Hit Damage (CHD).
I avoided focusing on Critical Hit Rate (CHR), since reload will proc the unique ability and fix the CHR at 100% for 2 seconds, and CHR modifiers aren't going to change much with a base CHR of 10%.
I avoided using Concentration Priority (in favor of Commando Marksmanship) because the reload penalty felt too high and limiting DPS, but you could get a little more CHD with Concentration Priority.
The only thing this really lacks is some kind of elemental damage type, but you could probably swap out Expand Impact Magazine for one of the elemental Enhancement mods. I just found that I was frequently running out of Impact ammo, which is why I chose that mod.