The 6.5-300 Weatherby Magnum
April 05, 2017
Weatherby's new magnum is the biggest, fastest 6.5mm cartridge in the world. You could call it a "Formula One" cartridge.
Named the 6.5-300 Weatherby Magnum, the new hot-rod round is simply the .300 Weatherby Magnum necked down to 6.5mm (0.264 inch).
Now, that's a significant step down, and since the bigger-bored .300 Wby. Mag. is already on the cusp of being overbored, it puts the 6.5mm version solidly into the realm of heavy horsepower. It's way past balanced, and efficient it is not.
But it is incredibly fast — as fast as the .22-250 with some projectiles — and its 6.5mm bullets are far more aerodynamic than any .22-caliber projectile. Those two characteristics give the 6.5-300 Wby. Mag. tremendous reach.
Initially, three factory loads will be available: a Barnes 127-grain LRX rated at 3,531 fps; a Swift 130-grain Scirocco II at 3,476 fps; and a Swift 140-grain A-Frame at 3,395 fps. Those are factory-advertised numbers, but my testing indicates that real-world results are very close.
For deer-size game, I prefer the Swift 130-grain Scirocco II bullet for the simple reason that it nips at the speedy heels of the slightly faster Barnes 127-grain LRX load and offers the highest ballistic coefficient (BC) of the three factory-loaded projectiles available.
Specifically, the 127-grain LRX has a BC of .485; the 130-grain Scirocco II has a BC of .571; and the blunter, flatbase 140-grain A-Frame has a BC of .401.
Although the lighter LRX bullet exits the muzzle of my rifle about 50 fps faster than the Scirocco II (3,499 fps versus 3,450 fps) when fired from Weatherby's factory ammunition, the slightly heavier, more aerodynamic bullet hangs on to velocity more effectively, which translates to less drop and drift at long range and more retained energy.
At my home elevation of 5,050 feet and in 70-degree temperatures, when sighted-in at 200 yards, the 130-grain Scirocco II drops 4.2 inches at 300 yards, 12.3 inches at 400 yards, and 24.7 inches at 500 yards, where it is still zipping along at 2,725 fps and packing 2,143 ft-lbs of energy.
That's darned near as much speed and energy as the popular 6.5 Creedmoor has at the muzzle.
Even better, zero the rifle at 300 yards, and the 130-grain Scirocco II will impact 2.0 inches high at 100 yards, 1.3 inches high at 200 yards, 6.7 inches low at 400 yards, and only 17.6 inches low at 500 yards.
While at first blush the 6.5-300 Wby. Mag. seems to be the perfect cartridge for long-range hunters, it does have a couple of drawbacks. One is that the cartridge is tricky to handload. (I'll come back to that.)
Another drawback is the necessity to use a tough bullet, which eliminates super-aerodynamic bullets like Berger's VLD Hunting and Hornady's ELD-X. I haven't had a chance to try Nosler's AccuBond Long Range (ABLR) in my rifle yet, but it may be a viable option because of its bonded-core construction.
However, I suspect Weatherby would have introduced a factory load with the ABLR had it proven capable of maintaining accuracy at 6.5-300 Wby. Mag. velocities.
If your 6.5-300 Wby. Mag. rifle likes the 130-grain Scirocco II load — and mine does — there's really no reason to worry about working up anything else for deer-size game.
If bigger-boned, heavier animals, such as elk or even really big wild hogs, are on the menu, you'll want to turn to an even tougher bullet. The Scirocco II performs spectacularly during impact speeds up to 3,200 fps and even a bit more, but during such fast impacts it will expand tremendously and hinder penetration.
Elk hunts are costly in terms of time, effort, and dollars, and you don't want to have to pass on a shot opportunity because your bullet won't penetrate enough on a quartering presentation.
If you plan to shoot beyond 400 yards or so, look to the Barnes 127-grain LRX. It's a superbly accurate bullet (in fact Weatherby's techs tell me it typically shoots the best of the three in the bulk of the 6.5-300 rifles they've tested), has a respectable BC, and even during very close-range impacts its shank holds together and punches deeply.
I shot a steeply quartering 200-pound hog with the 127-grain LRX at about 25 yards, and a postmortem showed that it performed in textbook fashion, causing tremendous internal damage and exiting the far shoulder.
For elk or moose inside 400 yards, I'd opt for the Swift 140-grain A-Frame. It carries a bit more weight and has tremendous integrity. It will hold together when impacting heavy bone at high speeds. Adam Weatherby shot a big 6x6 bull elk at 350 yards with the 140-grain A-Frame, and as you can see by the recovered bullet shown here, performance couldn't have been better.
Barrel life? What barrel life? Kidding aside, the 6.5-300 Wby. Mag. is high on performance but short on barrel life. My best guess is that shooters that baby their rifles, shooting no more than three-shot groups and allowing barrels to cool completely between groups, should get between 600 and 1,000 rounds before seeing a significant drop in accuracy.
Notes on Reloading
Efficient cartridges like the 6.5 Creedmoor, .308 Winchester, and so forth are typically mild-mannered and easy to reload. Severely overbored cartridges like the 6.5-300 Wby. Mag. are temperamental and take a lot of tuning to get just right.
A lot more powder is combusting, a lot more vibration is occurring, and a lot more speed is affecting the bullet. Throw all those consistency-affecting elements together and it's easy to see why the 6.5-300 Wby. Mag. is high maintenance.
Add in Weatherby's freebore — which has the great virtue of keeping pressures low at very high velocities yet complicates accuracy tuning — and you'll comprehend just how tricky the 6.5-300 Wby. Mag. is to handload.
Being aware that very overbore cartridges have a tendency to pressure spike when powder charges are reduced too much but vague as to exactly why, I put in a call to Ron Reiber, Hodgdon's ballistics guru.
According to him, the phenomenon typically occurs when the rifling leade becomes eroded and rough (which can happen within 80 rounds or so if a super-hot cartridge is shot aggressively) and when there's too much air space within the cartridge case.
It works like this: Excess air space can cause inconsistent or slow powder ignition. As the firing pin detonates the primer, if only a bit of powder ignites instantly, the bullet can be thrust lightly forward into the rifling leade, where it sticks tightly in the rasp-like eroded surface. (We're talking microseconds here.)
When the rest of the powder detonates, the stuck bullet resists accelerating down the bore just a bit too long, and excessive pressures can occur.
As long as internal case capacity is occupied close to 100 percent, powder granules are contained, held fast in the blast of the detonating primer, and ignite instantly and consistently, boosting the projectile through the rifling leade and down the barrel.
The takeaway? Don't download.
I wanted to include as many different projectiles as possible in this report, so I started with bullets other than the Swift and Barnes bullets factory-loaded by Weatherby when I began handloading the 6.5-300 Wby. Mag.
Except with Nosler's Partition (another inherently tough bullet), results were dismal. So dismal that I've not included them in the handload charts. Velocity extreme spreads were off the map, and accuracy averaged around 2.5 inches for three-shot groups.
My initial impression was that the rifle might have a bad barrel — very unusual in a Weatherby, but possible. Fortunately, the Nosler 140-grain Partition averaged sub-inch groups at 100 yards, restoring my faith. When production-lot factory loads with the Barnes 127-grain LRX and Swift 130-grain Scirocco II bullets arrived for testing, they put my handloading efforts to shame by averaging less than 1 MOA.
It appears that Hodgdon US869 powder is the 6.5-300 Wby. Mag.'s ticket to happiness. A charge of 91.0 grains under the Swift Scirocco II duplicated factory-load velocities.
My "factory duplicate" handloads with the Swift 130-grain Scirocco II didn't group quite as well as Weatherby's ammunition did, which I cheerfully attribute to a neck tension difference.
I couldn't immediately get my hands on any Barnes 127-grain LRX bullets, so I was unable to attempt to duplicate the factory load with that bullet, but I did work up a load using the Swift 140-grain A-Frame that more or less matches factory-suggested velocity, and it grouped right at 1 MOA.
After experiencing the broad extreme spreads, I've come to believe that neck tension is critical to consistent propellant ignition and resulting good accuracy since the freebore prevents bullets from being seated to kiss the rifling leade. Projectiles with a crimping groove or cannelure may offer an advantage, too, enabling careful handloaders to apply a crimp and prevent premature bullet movement that way.
On the subject of freebore, the designers of the 6.5-300 Wby. Mag. implemented a unique two-step leade into the rifling in an effort to assist bullets in maintaining concentricity across the long freebore jump. Only time will tell whether it's a valuable addition to the freebore concept.
Weatherby techs told me their go-to bullet — in any given caliber — for validating the company's accuracy guarantee is typically a Barnes all-copper TSX, TTSX, or LRX. It's just a theory, but my guess is that the tough, hard bullet jumps the freebore with less distortion than typical soft cup-and-core bullets do, leading me to think that possibly other monolithic bullets, such as Nosler's E-Tip and Hornady's GMX, should perform equally well.
I've heard claims that the 6.5-300 Wby. Mag. is moderate in terms of recoil.
Not in my world. Even with the relatively stout weight of the Mark V AccuMark (8.25 pounds), the cartridge bites. On paper, it kicks slightly less than the .300 Winchester Magnum loaded with a 180-grain bullet, but in reality, its recoil is so sharp that, to me, it feels worse.
I attribute it to the large amounts of powder being burned and the extremely high velocity exit of the bullet. But I wouldn't say it's truly vicious, and the cartridge's spectacular ballistics make it worth it.
That said, there's only one fastest factory 6.5mm cartridge, and it's the Weatherby.