I've been using corn sugar boiled in just enough water to make a thin syrup then swirling it into the beer as it siphons into the bottling bucket. I've had one batch where about 3/4 of the bottles were carbed fine, one batch where about half carbed fine, and one where carbonation was perfect throughout every bottle. I also stirred the beer and priming sugar a bit before bottling. Do I need to stir more? I noticed some of the bottle caps were a little crooked too, could that have been the problem?