For rolls
- Firearm ATK
- Critical Hit Rate
- Critical Hit Damage
- Element/Colossus/Weak Point/Rounds Per Mag
"Weak Point Expansion" can be replaced with "Dopaminergic Activate" for building it as allrounder.
Also you can remove element module and add "rounds per mag" module combining with "rounds per mag" from roll to reach around 15 bullets.