I'm not familiar with this kit but is the nib pushed in far enough? there seems to be a gap. It might just be the kit or the photo but apart from that, its a very nice pen. Well done.
One reason I found for the blank blowing when trying to turn closer to the tube is that the drilled hole is too big. Either try drilling the hole tighter or use some epoxy or thick ca to fill the gap. Others on you would probably be able to give other reasons but that's what I've found.