@Talyn - - Thank you for posting this. I replied in another post about how I came to be a "fan boy" of the 6.5 Creedmoor. Do I think that it is the be-all, do-all, end-all of cartridges? No I don't. It's all about bullet selection. Pick a bullet which will accomplish the desired task and use that. Push it out the muzzle at a speed which will allow it to perform as needed. Job accomplished.
For whatever mix of historical and technical reasons, the 6.5 caliber seems to hit that "sweet spot" of bullet length-to-caliber ratio in cartridges which fit well in various bolt actions without cramming the bullet too deep into the case. Also, the 6.5 cartridges, barring the bigger magnums, seem to hit the sweet spot of powder charge to bore diameter / bullet weight ratio, providing excellent internal and external ballistics. It does so without pounding the shooter with rifle recoil. Happy times!
I don't think that there is any "magic" in the 6.5 caliber. The 6.5 caliber enjoys the happy coincidence of the balance of the dimensions of available physical actions and the cartridges they are chambered for. This allows for an optimal bullet caliber to bullet length ratio plus an optimal ratio powder charge to bullet weight.
The same characteristics can be had in any other caliber. By caliber I mean bullet diameter, not cartridge denomination. However, too often the aforementioned ballistic characteristics get "out of whack" (a highly technical ballistics phrase) or the physical dimensions of the resulting cartridges prove less than ideal in available actions / magazines. Seeking the desired levels of balance between action length, magazine length, bullet caliber and length, cartridge case dimensions to allow "proper" seating, and case capacity for an appropriate charge of an appropriate powder has kept ballistic experimenters busy for decades.
On the topic of bolt action length, it took a number of years after the introduction of the 308 Winchester for rifle makers to create what we now know as a "short action". But the "short action" is too short for appropriate bullet seating in certain caliber / cartridge case combinations. And the old standard "long action" is noticeably too long for ideal fit. We now also have a "mini action" length available from a couple of manufacturers (CZ and Howa) that is perfect for the 223 / 6mm ARC / 6.5 Grendel / etc. Custom bolt action manufacturers are beginning to catch on and make a "medium action" that is a perfect fit for certain bullet / caliber / cartridge combinations. Having an action length that allows for "perfect" cartridge overall length without having to "shoehorn in" the cartridge fit or without a lot of left over extra space is very desirable in my book.
Also, keep in mind that ballistic performance goals have changed over the years. In former decades, the mantra of many was "more speed" in order to achieve flatter trajectories and greater terminal performance of bullets. In the most recent times, the focus has shifted to upping the game in terms of bullet technology by increasing BCs. The 6.5 has benefitted greatly from the success of these efforts. We are now seeing the fruit of what has been learned in other calibers as well. There is a similar trend of faster rifling twists and longer-for-caliber bullets developing in 25 caliber and in 27 caliber. But it was all started by the success of the 6.5!
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