Priming

Hi guy's
I have a few Questions about Priming sugars and priming methods. I brew in the UK using BeerSmith 2, I bottle my beer and I normally prime each 500ml Bottle with 1 measured tea spoon of Table Sugar.
My last brew I changed things. I batch primed using Brewers Sugar (Dextrose) 47g for 8 litres of beer  to cover 16 x 500ml bottles.  BeerSmith calculated 2.3 volumes of CO2 47g but my beer was very under primed.
Is Brewers Sugar (dextrose) the same as American Corn Sugar?
Do you need to prime with a lot more Brewers Sugar/Corn Sugar than Table Sugar?

I tried batch priming because I read it was easier and safer but I don't want waste another batch of All Grain due to poor priming.         

I prime with Corn Sugar.  I did a comparison on a recent batch to see what the difference would be.  This is for a 5 gallon batch primed at 2.3 volumes.

Corn Sugar = 3.93 ounces = 111.41 grams
Table Sugar = 3.57 ounces = 101.21 grams

For an 8 liter batch at 2.3 volumes, I got the following:

Corn Sugar = 1.26 ounces = 35.72 grams
Table Sugar = 1.15 ounces = 32.6 grams

I can't replicate your 47 gram calculation.

How long has the beer been in the bottles?  Is it a high gravity beer where the yeast may be a little stressed and just need some more time?

I think that you'll find that if you have patience, it will pay off.

I could be wrong on my calculations but putting one tea spoon sugar in a 500ml bottle gives a carbonation level of 3.6 to 3.7 volumes. Very high carbonated beer. Comparing that to a beer carbonated at 2.3 volumes would be a big difference.