I'd also suggest just buying the correct brass to start with if you are set on the 260. No sense in wasting time forming brass if you can buy it as needed. The 260 will get the job done target wise to 1K easily. A straight .243 is also really good with the right bullets.
Your purpose for the rifle leaves a lot of room though. How long of a range are you talking? Paper punching only or do you need to concern yourself with energy on target? Will this be shot prone only or a variety of positions? I could probably ask a lot of questions, but the purpose of the rifle needs to be explicitly explained for a proper cartridge selection.
Geb