Priming corn sugar, weight vs volume

The Northern Brewer priming sugar calculator says 3/4 cup of corn sugar weighs 5.3 oz.  The corn sugar I bought at my LHBS weighs 3.8 oz. for 3/4 cup (packed).  5.3 oz. is a heaping cup (packed).  Is there something funny about this sugar?

Did a heat-an-oz-in-oven test and reweigh.  Seems to be the anhydrous version of corn sugar.

I noticed the same thing. I was buying a very fluffy dextrose and some are more granulated. I stopped measuring by volume after that.

Nice, I was just getting back into bottling and that will be something to watch for.

Use table sugar (from cane or beets) and use 5/8 cup for 5 gallons, or 2 tablespoons per gallon.  Never have a problem again.

Yep, same here.