[Primed Cryo Rounds] is obviously hard to get, and replacing it with Hellfire saves you a forma and 40,000 endo
(The DPS only drops from 129,000 to 93,000)
The endo cost looks steep, but it's all in the Serration, Heavy Caliber, and Primed Cryo Rounds. Keeping them a little under-leveled is fine
(Don't worry about the accuracy debuff, it doesn't matter for this weapon)
Replacing Serration with Amalgam Serration only reduces the DPS by 3% so the sprint speed could be preferred if you have enough endo
If you want to equip an Exilus mod, I'd recommend [Cautious Shot] to reduce stagger or [Vigilante Supplies] for the extra crit