I'm rereading Lee's "Modern Reloading". He mentions that reusing fireformed cases in the same (bolt-action or single shot) rifle they were shot in leads to greater accuracy, all other things being equal. He contrasts this with full-length resizing. Why is this? Does it make a better gas seal? If so, then I assume that means higher velocity. So is this just a case (no pun intended) of higher velocity leading to better accuracy, or is there something I'm missing?