The above website might have some info for you.
Every barrel is unique. You can only generalize about external ballistics when thinking about barrel length. You posts begs the question of what is "reliable" information. Unless you actually chronograph your particular handgun with a particular load, you will never know.
The various factors of a barrel other than length which may effect bullet velocity (that I can think of off the top of my head) are: bore smoothness, uniformity of diameter of the bore, depth of rifling, type of rifling, barrel to cylinder gap (if any), free bore (if any), and twist rate of rifling.
In general I would consider the 2" barrel ballistics and be happy if you actually got any real increase. In a short barreled handgun a few % increase or decrease in velocity is not all that important.
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