I don't have any experience making 260Rem brass but have made a bunch of 264WinMag brass out of 7MMRemMag brass. All I do is either run the 7Mag brass through my FL 264 die or my 264 neck sizing die and they are ready to load. I don't know if 308 would give you thick necks or not, you might try a couple and measure the outside neck diameter and compare them to any 260 necks if you have any. BTW, I don't know what lube you use for sizing but I would highly recommend Imperial Sizing Wax for this type of sizing as it is recommended for case forming.