For the 1,000,000th time, don't add sugar directly to the bottle. Calculate how much sugar you need for your entire batch, boil that with a bit of water, then pour the sugar water into your bottling bucket before racking your beer into it. For most 5 gallon recipes, 3/4 cup of corn sugar and 1 cup of water is recommended.
Gotta disagree with this statement. Its usually from bottling too early.Adding sugar directly to the bottles is probably the #1 culprit behind bottle bombs. It's almost impossible to get the exact amount needed into each bottle.