I have done various 308, 243win and 260win brass conversions to 6.5cm. Federal is soft and doesnt last and isnt worth all the work required to convert it. 1xLC 7.62 will last much longer than Federal. You need to push the shoulder back to 6.5cm measurements, you need to trim to length, you then need to use a neck turning mandrel and then turn necks as the neck will be too thick for 6.5cm. You will then need to size the neck for .002 (or whatever you want) neck tension after neck turning. Then fireform to finish setting the shoulder (fireforming loads are still just as accurate as formed loads). I did this to 250pcs of 1xLC for my 6.5cm semi since it beat up Hornady brass pretty good and Im not shooting expensive Lapua or similar out of it.
Winchester branded 243 brass only needs to be pushed back, trimmed, neck sized and fireformed. The thinner neck doesnt require turning. But this brass did not hold up nearly as well as Lapua 308, 260rem or LC 7.62 with pockets going pretty quickly.