Going to build new F-class rifle and looking at the 260 ai. Which would be the least amount of prep time. The 308 Lapua necked or the 243 Lapua necked up? I read the article on the Accurate Shooter about the 243 Brass leaving a donut when necked up. Will the 308 brass do the same? What about sizing the 243 brass to 7mm, then back down to 6.5 would I still have the donut problem?