Okay i see a few reasons now why my numbers are different:
1) I did forget the Penetrate perk with the AP ammo. Fixed
2) You're figuring DT as a per bullet thing, whereas I figured it as a total per burst.
3) It looks to me like you also figured he has basic Toughness in addition to the perks he specified, whereas i left basic Toughness out.
4) Formula order is very different. You start with avg base dmg but go straight to multiplying by ammo dmg mod, whereas I go straight to adding extra dmg from BRD perks. Next i go to number of bullets multiplier in order to get a total dmg, whereas you don't multiply number of bullets until last step after factoring in DT and DR per bullet.
Once again, thanks for the help, Seki!