Re: Just got a 6.5 blank. Chamber Ideas?
It all depends on how you'll use it.
260 has both cheap and Lapua brass, but you either lose case capacity or run into magazine length constraints shooting the longer bullets. Factory match ammo is out there from several manufacturers, but it is on the expensive side.
6.5x47 has great brass, no cheap brass option if you shoot matches where you can't collect, no length issues. Factory match ammo is crazy-expensive.
6.5CM has decent brass, but no option for Lapua, no length issues. Factory match ammo is only slightly more expensive than buying Lapua brass for the other two!
I'm thinking of giving the Creedmoor a try. I handload, but sometimes I just don't feel like it, or don't have the time to make enough before a match. Leaving Lapua brass on the ground doesn't interest me, and I like having bullets where they need to be without worrying about magazine length.
It's all in what you're going to do with the rifle and how much you're affected by brass/ammo costs. A few have mentioned going to 6mm, and that may be a great option if you shoot a lot of paper, but hits on steel at distance are harder for ROs to spot (and score). If you shoot matches that are primarily steel, I'd stick with the 6.5.