I remember stressing about this and asking on here too years back
Time to pass it on
Your firmented beer will contain some Co2 disolved in solution from the firmentation. Basicly its very very lightly carbonated. When the beer hits the dex in the bottle, it releases this gas and it froths. Some beers will have more or less gas in solution, depending on weather you racked it, how long it has sat since the firment finished ect.
The best way to bottle and achieve a cosistant carbonation level in the bottle is to bulk prime
some info here
http://www.grumpys.com.au/m1.php3?manualid=13
I rack to a clean sterile firmenter from the primary firment and leave for a week off the yeast cake to clear out and finnish off completly.
I then rack back to the first firmenter (cleaned out and steralised) and mix in my bulk priming solution of dex disolved in a few hundred mills of boiling water. It froths a bit in the firmenter but thats just the gas comming out. now you can bottle it, without having to put anything in the bottle and it fills to the top first go with no froth.
I took lots of data from many beers, over and under carbed and figured there had to be a mathamatical way to work out how much dex to use for a given amount of beer.
It seemed to me that as the final gravity dropped, i needed more priming sugar to give a certain carb level in a certain volume.
I made up a table and you can see it used roughly on the link above..... i posted it on there years back when i worked it out.
here is the full version
FG - Priming amount 22 liters
1.004 - 170
1.005 - 165
1.006 - 160
1.007 - 155
1.008 - 150
1.009 - 145
1.010 - 140
1.011 - 135
1.012 - 130
1.013 - 125
1.014 - 120
1.015 - 115
1.016 - 110
1.017 - 105
1.018 - 100
1.019 - 95
1.020 - 90
all amounts are for dex..... not surcrose
If you want more gas.... up it by 10g in the batch and see how it goes.
simple as that.
any more questions, just ask
Bulk priming will change your life if your stuffing around with priming bottles of incostant lollies
cheers