Some bullets make it thru the transonic region better than others but most have problems and this does nothing positive for accuracy. Most long range shooters know all about this and they make sure their loads stay above the transonic region. A good example is the 168 SMK which was a favorite for XTC to 600 yards for many years but when they are shot at 1000 yards they go subsonic and even key hole sometimes. I have pulled targets where these bullets were shot and sometimes they even scored well on the conventional prone target but many times they were erratic and some key holed.Bullets do not become unstable when moving below the speed of sound. If they did, there would be no long range shooting.