I just got the optimized bullet count build
capped out at 150+ bullet count when above half hp (my max hp was around 370)
reaches 650000+ (yes, six hundred fifty THOUSAND) dps on the counter (but goes back down because the fancy heart charm's 60 heal per second doesn't work)
even better, using the helix barrel's second enhancement, you get x2.5 bullet count after using underbarrel, so the theoretical limit of this gun is 375 bullets
Build specifics:
shotgun chassis
quad helix
withered heart charm
the blood mag upgrade that gets you 3x bullets when above 50% health
everything else is just personal preference
tuning priority:
1. anti safe selector (perfectly built for this gun, gives you more bullet count and regen)
2. slickshot springs (reload speed is always good, and gives a much appreciated healing boost)
3. nanobot coating (increases the damage of the reverse counter mechanic given by hemolytic mag)
4. cold forged casings (increases the amount of health, so more time at >50% health = more bullets)
edit:
energy blaster is best under barrel, takes most advantage of helix ring 2.5 multiplier
homing sight does worse than the tech module
because tech module is better, outlaws rifling now replaces cold forged casings at 4th best tuning
frost turbine/eye of horus/cold forged all tie for fifth, fros turbine is better for helix ring, eye of horus to increase crit rate