6.5cm can be made out of 308 brass just like 260 can. Ive made 1000+ out of LC 308....Very very nice stuff but yes necks need to be turned. You can do it.
Im not sure about in your AO, but 6.5cm brass is EVERYWHERE around me in PA. Same with 6.5cm ammo.
The #1 reason 6.5cm is the clear winner for a large frame gasser is because you can run all the long 140gr bullets out of a mag with a 6.5cm SAMMI reamer and touch the lands and still have room in the mag. That IS NOT possible with 260rem.... You can run 260rem, but you need to push that 140gr bullet way down in the case to fit in a mag then you have a big jump to the lands when using a 260rem SAMMI reamer. Looking at my notes, a 140 your looking at 2.92" to the lands... So to fit in a mag at MAX coal its a .1 jump on a new barrel. Now, their are custom 260rem gasser reamers out there with a shorter freebore but you have to have a custom barrel spun up by a smith and request that reamer, if they have it... You arent finding off the shelf 260rem AR barrels like that.
So, no special reamer/throat to run the long 140gr 6.5cm rounds out of a mag... Need special reamer to do that with 260rem..
Now, those of us that built dozens of these, 260rem first, 6.5cm rifle gas, 6.5cm +2....We ARE NOT running Magpul mags. We are running KAC and Larue mags that allow you to run rounds with a COAL up to 2.871".... With 140 ELD's in my 6.5cm SAMMI chamber AR's, I hit the lands with that bullet @ 2.857..... Plenty of room to chase if I wanted to....I run .02 off lands...