Two high velocity, high energy, and small bullet diameter cartridges are the 6.8 Western and the 6.5-300 Weatherby. Both these rounds have their reputation for being effective against big game and often times, these rounds are in the same market as each other. With that being the case, it would only make sense to compare these two cartridges to see which is better and why.
Here is the short answer:
The 6.5-300 Weatherby has more energy, less drop, less wind drift, and shoots at higher velocities when compared to the 6.8 Western. However, the 6.8 Western is less expensive, has less recoil, and is more popular than the 6.5-300 Weatherby.
Now that we have looked at the short answer, we can look in-depth at each cartridge, their ballistics, and how they compare in depth.
6.8 Western
The 6.8 Western is a newer cartridge introduced by Winchester and Browning. It was designed to be a high power short action western hunting cartridge for hunting elk and moose. It has similar ballistics to a 270 WSM if not slightly better.
The 6.8 Western is a fairly versatile cartridge that is good for hunting elk, moose, deer, sheep, and goats. Where it really shines is shots past or around 500 yards as it has a very correctable amount of wind drift and drop. If you want a good western game hunting cartridge this would be one you want to look at.
There are two main downsides to the 6.8 Western: The first is that it is a newer cartridge, so it is going to be harder to find ammo, and the ammo that you do find will often be quite expensive. Secondly, the 6.8 Western has a pretty hefty amount of recoil that can be difficult for some shooters to handle.
Here is a ballistics chart of the 6.8 Western with a 160-grain Winchester Accubond LR:
| range (YD) | drop (IN) | wind drift (IN) | velocity FPS | energy ft-lb |
| 0 | -1.5 | 0 | 2970 | 3134 |
| 50 | -0.2 | 0.1 | 2893 | 2973 |
| 100 | 0 | 0.4 | 2817 | 2819 |
| 150 | -0.9 | 1.1 | 2742 | 2672 |
| 200 | -2.9 | 2 | 2669 | 2531 |
| 250 | -6.2 | 3.1 | 2597 | 2396 |
| 300 | -10.7 | 4.5 | 2526 | 2267 |
| 350 | -16.5 | 6.2 | 2456 | 2143 |
| 400 | -23.8 | 8.2 | 2387 | 2024 |
| 450 | -32.7 | 10.5 | 2319 | 1911 |
| 500 | -43.2 | 13.2 | 2253 | 1803 |
6.5-300 Weatherby
The 6.5-300 Weatherby is a newer round made by Weatherby by taking a 300 Weatherby magnum case and necking it down to use a 6.5mm bullet. This creates a cartridge that shoots a light bullet at extremely high speeds which can take game as big as elk.
The 6.5-300 Weatherby has a lot of energy, however, it is often not used on game larger than elk because of its small bullet diameter. But on game like elk, deer, and pronghorn, the 6.5-300 is a great cartridge.
There are two main downsides to the 6.5-300 Weatherby: The biggest problem is its short barrel life. Most barrels will only make it 800-1000 rounds before they will need to be replaced. The second problem with this round is that it does have a lot of recoil so it will be hard for most shooters to keep shooting accurately.
Here is a ballistics chart of the 6.5-300 Weathebry with a 130-grain jacketed soft point bullet:
| range (YD) | drop (IN) | wind drift (IN) | velocity FPS | energy ft-lb |
| 0 | -1.5 | 0 | 3425 | 3386 |
| 50 | -0.4 | 0.1 | 3332 | 3204 |
| 100 | 0 | 0.5 | 3241 | 3031 |
| 150 | -0.5 | 1 | 3151 | 2866 |
| 200 | -1.8 | 1.8 | 3064 | 2710 |
| 250 | -4.1 | 2.8 | 2978 | 2560 |
| 300 | -7.3 | 4.1 | 2894 | 2418 |
| 350 | -11.6 | 5.6 | 2812 | 2282 |
| 400 | -17 | 7.5 | 2731 | 2153 |
| 450 | -23.6 | 9.6 | 2652 | 2030 |
| 500 | -31.4 | 12 | 2574 | 1912 |
In-depth comparison
Ballistics: The 6.5-300 Weatherby is the better cartridge. This is because of its larger case size and lighter bullet weight. However, some hunters prefer the 6.8 Western because of its better ability to expand on impact and the fact that it is less likely to fragment due to too high of velocities.
Recoil: Because of the larger case size of the 6.5-300 Weatherby, it is going to have more recoil than the 6.8 Western. This is going to make it more difficult to shoot over long periods of time or for smaller frame shooters. However, this is not the say that the 6.8 Western doesn’t have its fair share of recoil too.
Cost and availability: The 6.8 Western beats the 6.5-300 Weatherby here. This is because the 6.5-300 Weatherby is not a very popular cartridge which means it will be more expensive and harder to find than the 6.8 Western.
Versatility: Again the 6.8 Western beats the 6.5-300 Weatherby. The 6.5-300 Weatherby has too much energy to hunt smaller game like deer without a lot of bloodshot meat. Additionally, the 6.5-300 Weatherby has a small bullet moving so fast you run the risk of it fragmenting on impact on larger game rather than expanding as it should.
Barrel life: Yet another area where the 6.5-300 falls behind is barrel life. Generally speaking, the 6.8 Western will have a longer barrel life than the 6.5-300 Weatherby by 500-1000 rounds. However, how long a barrel will last is heavily dependent on how you treat it, (I.E. how often you shoot and how many rounds you shoot in quick succession)
Conclusion
When it comes to ballistics, the 6.5-300 Weatherby will be the better round. However, in every other metric you can measure a round by, the 6.8 Western will be the better cartridge.