Well, in regards to taking a shorter, smaller round with less case capacity but the same size bullet and saying it will do the same or better......at some point I think it might be a good idea to consider that Alliant, Hornady and Sierra are all trying to sell you something, and it's not the 260.
One thing I have learned about cartridges and reloading, trust no one or nothing but your chronograph. You might not always like what it has to say, but it's the only one that's not "pre-skewed" for "other" reasons....
"only reason"...what about sizing readily available quality 308 brass in one easy step??? What about a bigger case capacity {in spite of what the salesman are telling you}????
Why would Sierra care whether they sold me bullets for a Creedmoor or a .260? Same with Alliant and powder? Alliant still hasn't published that 6.5 data on their website, and I requested and received the PDF over a year ago! Plenty of loads up for the dying .260 on their site though, sounds like they're really pitching the Creed hard.
What bullet or powder makers show a velocity advantage for the .260 over the 6.5? Are all load books conspiring to trick everyone into shooting 6.5s?
My Chrono does match very nicely with the Alliant and Sierra loads, 140gr ABs exit my 22" hunting barrel at 2,760 fps using RL16. 127gr LRX exit the same rifle at 2,910 fps. Powder weight wise, there's not even much difference in the loads I use for the 6.5, and the loads the few people I know shooting the .260 are using for PRS type matches.
What's the net capacity after you load both cartridges to 2.8"? Is the useable case capacity really larger after you stuff most of a127gr LRX, 143 ELDx, 147 ELDm, 150 SMK, or even some of the lankier 140gr bullets down into the .260 case?
Hornady, Lapua, Nosler, Norma, Federal, Sig Sauer, Peterson, Starline x2 all make 6.5 brass. Why would I ever care about forming something from .308?