magazine size is calculated like this:
1. your actual magazine size
2. additive number from extended mag accessory
3. the number above multiplied by the sum of all mag cap % from your mods/blueprints/procs/attributes and rounded up
so for crossbow its just 1 arrow x mag cap, and everything at or over 50 will round up to 2 arrows, but if you stack 150% you would have 3 arrows
The optimal way to reach 150%+ mag cap would be:
6x 12% mag cap roll mods
1x 9.6% mag cap roll mod
helmet mod must be magazine capacity +30% when reloading with empty mag
4p renegade set (if half of your hits or more will be weakspot dmg it will give you 30% magazine capacity)
1p lonewolf 10%
and shaman vulture top chest piece (very good because of unstable bomber procs)
The build I was using is what I could get to reach magazine capacity threshold, it is by no means optimal, this was to test the concept if its possible, would require a lot of optimization
Your ideal mods would have:
1. magazine capacity (mandatory)
2. reload speed (very very helpfull)
3. crit hit dmg (you will crit a lot, especially withs shaman vulture top)
4. status/elemental dmg