« on: February 24, 2016, 11:45:19 AM »
you won't need to force carb the keg. you will need to let the remaining priming sugar ferment out though. once that happens the keg will be carbonated. However, for some reason that is not readily explainable, a large volume of beer requires less sugar per floz to achieve a given carbonation level than a small volume of beer. So for 5 gallons of beer to be bottled in 12 or 22 floz bottles you generally use ~4 oz of sugar. but for the same volume of beer in a keg, to naturally carbonate requires more like 3 oz.
I believe the difference in priming sugar amounts between kegging and bottling is due to head space. In bottles, a larger percentage of the container is head space compared to beer volume. In a keg this percentage of head space is lower. Thus less CO2 is needed to fill that head space in a keg. And less CO2 means less priming sugar.