Just a quick re-cap.

I believe the 6.5X284 is 100% fad and really had no merit outside what the 6.5-06 has to offer in actions and in performance in both game field and target range. It is effectively about the same, but cost more to make and more to shoot.

The new 26 Nosler is also a fad, trying to go super fast with high BC bullets and it does this well. But bore life is super short, even shorter then the 64 Win Mag, and the Win mag is just as accurate. In fact I have seen 4 26 Noslers now and none of them are quite as accurate as the only 264 Win mag I now of around here, one I did a re-barrel on for a neighbor about 5 years ago, which shoots into 5/8" All the 26 Nos gun I have seen 9only 4 so far) shoot well, but not 5/8" well.

The 264 was a fad and is barely hanging on today. The nail in its coffin was the 7MM Rem mag and the 270 Winchester that it was trying to replace. The 7 mag did all it would do and do so better with a larger selection of bullets and the 270 was too well entrenched to give up ground. Number don't impress someone that has 50 years of excellent success. In the 50s when the 264 came out the 270 was very very VERY well received already and the market was not primarily target shooters, but hunters. If men of my Dad's age had 100% satisfaction since their dads were young, and you offer them something that's "better" they are going to ask better for what? And how do you get better than a 100% satisfaction? So the 264 got off to a late start and then Remington cut it's throat with the 7MM Mag, so the 264 was a good thing offered at the wrong time, and that fad started out but never got a lot of traction.

Now the 26 cal cartridges that really have merit are the old 6.5 Swede, the 260 Remington and the new 6.5 CM I wrote about above. All are close in performance.

The 6.5X55 is the standard to which others are compared. It is the one to match and beat. In International Military Matches all the way up through the 90s (I stopped my involvement in the late 90s) and maybe even today, it's the shell that is "the one to beat" and beating it at 600M 900M and 1000M is a hard trick to pull off. Even our Hot American Magnums don't beat it often. Americans often loose those matches because they send too much time and attention of trying to come up with a "better" shell or bullet and don't simply shoot and shoot and shoot, so they lack the degree of skill they need to win. American love to compare theories and parade around their tables and mathematical formulas, but none of that matters to the man laying on his belly shooting, especially if that shooter is using a rifle with it's 20th barrel in it, (19 of which were shot out in the last 10 years.) That's not a theory. I have seen that with my own eyes a number of times. We American always seem to think "new and improved" is new and improved and in most cases it's not. In many cases it's a step backwards.

But the Swede doesn't fit in modern NATO length magazines however. For a mid length or long bolt action, loaded one at a time from the top, it's still the king of 6.5s.

Enter the 260 Remington.
308 necked down. Does all the 6.5X55 will do if the magazine will allow seating the same bullets without deep seating and encroaching on powder room. But not all guns allow this. It is just as accurate and a very good hunting round. It's popular especially in new rifles that come set up as 308s to start with, so a 26 cal option is a drop in. As a custom gunsmith, I see the demand for it, but even to this day I get calls for 6.5 Swede about 2 to 1 over 260 Remington. The main demand I get for barreling to 260Rem is from those using 243s that want to step up a notch in power, and not buy a new gun. That's it's real market so far, in my shop at least. It's an excellent option too.

So enter the 6.5 CM.
Now this one is the correct combination for case shape for use in NATO length mags, will come close enough to the Swede in use of hunting bullets to not matter in the field, and is set up from the drawing board for the use of the very best target bullets, and wills till fit the NATO length mags.
This is the one I think is going to go through the fad stage and become the new standard. This one, in combination with the rifles it's made for, will be the new 6.5 of the future. I am betting the Swede will give up ground to it over time. I also expect it may start to take over the 260 Rem market too. Not because it's any better then the 260 for hunting, but as it gains popularity the availability of factory 260 ammo may decrease.
For the hand loader (most of my customers) the 260 will not be moved because NATO machine Gun brass is cheep and sometimes free, and it's very easy to make into 260 brass. The CM s based on the 30 TC, so you can't make it from 308.

So I am betting the three 6.5s we'll see on top of the heap in the next 20-30 years are going to be the 6.5 Swede, the 260 Rem and the 6.5CM. Today, that is the order of demand too.

In a few years I expect that order to be exactly reversed.