And yet another...

https://gundigest.com/gear-ammo/reloading/greatest-cartridges-6-5-284-norma-long-shot

Back in 1963, the cartridge designers at Winchester introduced a new cartridge to the marketplace. Dubbed the .284 Winchester, it was designed specifically to produce ballistics equal to the .270 Winchester and .280 Remington, but in a case that was the same general length as the .308 case that would fit in the Winchester Model 100 autoloader and the Winchester Model 88 lever action rifles.

They succeeded by designing a rebated rim case with a greater diameter that provided a powder capacity about the same as the .270 and .280.

Although the designers met their design goal, the cartridge, and the rifles it was designed for, turned out to be considerably less than a smashing success. Savage made a few Model 99s in that chambering, and Ruger also did a run of M77 rifles chambered for the cartridge. To my knowledge, no other cartridge manufacturer except Winchester ever loaded the cartridge.

By all reasonable measures, an unpopular cartridge chambered in relatively unpopular rifles, and available from only one source, should quickly disappear from the market. The .284 Winchester cartridge was headed in that direction and would have made it there quickly had it not been for one factory.

Wildcatters found the case design suited the development of a few very useful non-standard cartridges, primary of which was the 6.5-284, legitimized by the Swedish ammunition maker Norma in 1999 and renamed the 6.5-284 Norma cartridge. The reason — the cartridge found its niche among long-range target shooters.
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I am told that these days it is the most widely used non-wildcat cartridge in F-Class and 1000 yard benchrest matches. For awhile, a variation of the 6.5-284 Norma held the 1000 yard benchrest record of 1.564 inch! That record was broken (group size 1.403”) in 2007, but the cartridge is still very popular with long-range competitors.

It is slowly gaining an inroad into the hunter’s market as well.
For awhile, a variation of the 6.5x284 Norma held the 1000 yard benchrest record of 1.564 inch!
For awhile, a variation of the 6.5×284 Norma held the 1000 yard benchrest record of 1.564 inch!

The 6.5mm chambering in various forms have long been popular in Europe and in Africa, but have gained acceptance in the US market very slowly. The US sporting market aversion to any cartridge designated with a mm following it has long had a very hard row to hoe among American shooters. That seems to be changing however.

Even my old pal and fellow curmudgeon David Petzal, seems to have taken a liking to the cartridge. Dave, for those readers that have been languishing under a very large rock for a half-century or so, has been writing for Field & Stream since the era of the quill pen and ink well. He has, during those many decades, earned the enviable reputation of not liking much of anything. However, even Dave wrote a two-part review of the 6.5-284 Norma in his Field & Stream blog that is reasonably favorable. Reasonably favorable from Petzal would be the equivalent of a gun-wrenching, wall climbing, flag waving, brass-band booming hoopla coming from anyone else.

He found the cartridge capable of extreme accuracy, while delivering the goods with light recoil. Typical of Petzal, he also wrote, “And one other fringe benefit: If, when someone asks you in hunting camp what caliber your rifle is, and you say “6.5-284,” people will have no idea what the hell you’re talking about and will think you know all about guns and shooting. I’ve been dining off this for years.”

I sure wish I had come up with that one!
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NORMA's take..

http://www.norma-usa.com/index.php/produ...e-month-6-5x284

Excerpt:
The same phenomenal external ballistics that endear the 6.5-284 Norma to many die-hard long-range competitors also interest a budding breed of hunters who excel at stretching the distance when situation dictates such. For a “mountain” or “African plains” rifle, where shot distances can be exponentially long, there’s likely no better choice; in fact, when loaded with streamlined hunting projectiles, the 6.5-284 Norma outperforms the vaunted 270 Win. at distances beyond 400 yds. For example, when loaded atop of 47.5 grs. of Ramshot Hunter, a Swift 130-gr. Scirocco II—with a BC of .571— propelled to 2,949 f.p.s. from the 26” barrel of my E.R. Shaw Mark VII rifle drops 3.4” at 300 yds.,14.6” at 400 yds. and 32.2” 500 yds. when zeroed at 250 yds. Despite its 3,250-f.p.s. muzzle velocity (factory-provided ballistics) the 120-gr. Kalahari from the 270 Win. Norma-USA American PH load drops 3.4” at 300 yds., 14.9” at 400 yds. and 34.4” at 500 yds. with the same zero. The key differences, however, are that the 6.5-mm bullet has an additional 448 ft.-lbs. of energy at 500 yds., and it deflects off course 11.7” less at the same distance when encountering a mild, 10-m.p.h. full-value wind. Such performance is why serious long-range competitors and hunters “pay to play” with the 6.5-284 Norma.