Just pick you case, .221, .222, .223 or .222 mag, and your bore dia. 6mm. 6.5mm., 257 or even .30 cal. I have a .25 cal. on the .221 case which is a good shooter but I may punch it out to the .222 mag. case. I also have a 6 mm on the .222 mag. case ( 6 x 47 ). It is a real tack driver, but it`s a 13 lb. bench gun. A hint to save you money. If your go with one of these rounds you can go up or down 2 bore sizes with the Redding S bushing dies. These are excellant dies and while alittle expencive, they are still about 1/2 the cost of custom dies.