Originally Posted by Toy4Rick
So how do we explain why my English Porter was under carb'd with nearly 5oz of corn sugar when the calculators indicate to use 3.4-3.6oz?
Priming calculators are based on the temperature you have fermented the beer. Depending on the temp, the level of residual CO2 varies. Yes, there is CO2 in the beer before you carbonate! A simple "one amount carbonates all" solution isn't accurate. Shame on your HBS.
If your two beers' fermentation temps were different (and attenuation as well!), then you will get a different finished carbonation with different beers even though you use the same amount of sugar for priming.