You have B99s (10,900 MTOW and a max ramp weight of 10,955) and C99s (11,300 MTOW and a max ramp weight of 11,380). A typical B99 in a cargo configuration weighs roughly 5900 lbs. If you add 2466 lbs for max fuel and a 200 lb pilot you end up with 2389 lbs of useful load. A C99 weighs roughly 6300 lbs in a cargo configuration. Add the same 2466 and a 200 lb pilot and you end up with a similar useful load...2414. You do get variations in weight per aircraft. I've seen full fuel useful loads up closer to 2500 lbs depending on the particular plane. At my company most of our C99s have an under-fuselage cargo pod that adds quite a bit of volume for bulky loads. With what we carry we usually bulk out before we reach MGTOW.