I use the hammerhead barrel on mine with the autococker fins. The .686 seems the best to me for first strikes. It makes a huge difference for first strikes, if you use a smooth bore, it seems to take about 20 yards for the round to stabilize. The hammerhead is designed to work with regular paintballs and although rifling doesn't really seem to help them, it doesn't seem to hurt them either. I've found that with the .686, when I chrono with Nelson Anarchy, the first strikes are only a little faster which works great because if you turn the velocity up to much with the rifling on the hammerhead, it will start to cause the balls to curve.