The 6.5mm cartridges have surely caught on in the last decade or so, and now they're available in all shapes and sizes from the small to the tall. The 6.5mms have been with us since the end of the 19th century—in the 6.5x55mm Swedish Mauser—and the fast 6.5s have been with us since the 1950s in the form of the .264 Winchester Magnum, and a bit later in the form of the 6.5 Remington Magnum. The .264 Winchester had the lion’s share of popularity; it was—and still is—a fast, hard hitting and accurate cartridge; however, Remington’s 7mm Magnum came on the scene, and stole the .264 Magnum’s thunder.
Fast forward to the 21st century, and the 6.5mm revival is certainly on. The .260 Remington, the 6.5 Creedmoor, the 6.5-284 Norma, the 6.5 Grendel; all are effective in the field and easy on the shoulder. However, we here in America have an undisputable obsession with speed, and it wasn't long before the fast 6.5s came back to the surface.
Nosler brought their first proprietary cartridge to light at the end of 2013; the .26 Nosler was the most powerful 6.5mm cartridge, launching a 140-grain bullet at 3300 fps, bettering the velocity of the .264 Winchester by 100 fps. The .26 Nosler is based on the excellent beltless .404 Jeffery case—blown out to increase case capacity—with a rebated rim, yet shortened to 2.590″ so it will run in a standard .30-06-length action, offering a case capacity of 93.5 grains of water. Bottom line: the .26 Nosler is a shooter, even if it is hard on barrels. This is not a long-term target cartridge, though the down-range ballistics are excellent, barrel life is simply too short for extended range sessions, and the recoil is too much for the average shooter to spend the day with. However, as a hunting cartridge, it shoots flat and hits hard.
Weatherby’s dog in this fight is a big dog, snarling and barking. The .300 Weatherby has been the flagship of the fleet, and it was perfectly fitting that they used the .300 as the platform for their 6.5mm cartridge. The 6.5-300 Weatherby Magnum is a beast; it is the .300 Weatherby Magnum—requiring a magnum-length action—necked down to hold 6.5mm bullets, replete with the double radius shoulder that Weatherby is famous for. Roy Weatherby began experimenting with the full-length Holland & Holland case in the 1940s, and he actually had a 6.5mm cartridge, but it would be 2016 until any Weatherby 6.5mm cartridge would see the light of day. The 6.5-300 Weatherby Magnum dials up the heat another 100 fps over the .26 Nosler; it’ll launch the 140-grain bullets at a muzzle velocity of just shy of 3400 fps. It uses a 2.825″ case—just a whisker shorter than the parent .375 and .300 H&H cases—with plenty of case capacity; 98 grains of water to be specific.
To be honest, both cartridges are overbore, in that the amount of powder to be burned is greater than the capacity of the usual barrel length, so efficiency is a non-issue. Additionally, both of these fire-breathers will be hell on a barrel’s throat, just as the .264 Winchester Magnum is, so a purchaser needs to be aware of that heading into the deal. Furthermore, both of these cartridges are proprietary; at the time of this writing only the developing company is producing factory ammunition. So which of the two makes more sense for a hunter who desires this level of performance?
I feel the .26 Nosler takes first place among these two, for a couple of reasons. Primarily, there are many more rifle makes and models available in .26 Nosler, including the Browning X-Bolt, in addition to the Nosler rifles. The 6.5-300 is available in several Weatherby models, but not from any other company. While the Weatherby rifles are high-quality and have a large following, there are simply fewer choices. Secondly, ammunition and components for the 6.5-300 Weatherby Magnum are going to be more expensive than for the .26 Nosler.
Both cartridges offer a highly useable long-range trajectory, and at this level of velocity, I’m not sure that the 100 fps gain in the Weatherby cartridge will make a significant difference. I've also found that both cartridges are wonderfully accurate; I’ve had both cartridges exhibit sub-MOA performance. I will, invariably, recommend the strongest bullets you can get, especially if a shot inside of 100 yards were to present itself, as the high impact velocities will definitely test the strength of any cup-and-core bullet. Brass life for the .26 Nosler should be longer than that of the 6.5-300, as the Nosler design lacks the belt of brass, and the case stretching and thinning associated with it.
While neither choice will be inexpensive to feed, there is something fun about having the fastest cartridge in its class, and both the .26 Nosler and 6.5-300 Weatherby Magnum are in the top tier.