I am using International Clays in a STS hull. Ran out of Remington primers and have Winchester 209. I was getting 1180 fps with the Remington primers with a charge of 18.8 grains. If I use the 20.7 on their web site, it is way over 1200 and they really kick. So, It looks that I have to reduce the load with Winchesters. Question is, how much to use. BTW, the velocities were with a chronograph.