This is not a tough question to answer if you have a bit of knowledge about reloading. When it comes to reloading, you need as much accuracy as you can! For ultimate accuracy, you will need the best bullet along with good grade power. Also, the good quality calipers are capable of providing you an accuracy of 0.001 inches to more than 6 inches. Usually, the accuracy will be .0001 inches for 150 mm calipers. In some cases, the measurement is more than this.