I'm new to the game. Have been shooting prairie dogs w/22-250 @ 4000 fps and 257 STW @ 3900 - 4000 fps. Lately have been shooting metal plates w/guys shooting 308 and 6X @ 2700 - 2800 fps. VERY impressive shooting. Can someone explain why the 6XC over the 243? Does it have something to do with case volume vs powder charge volume? It can't be simple, but any explanation will help. I'm wanting to have a 6XC built and need a little info to "push me over the top". Thanks