The 5.56 NATO cartridge has long been the dominant choice for tactical rifles. A recent trend away from this pattern has drawn shooters to larger-diameter options. Suspected reasons for this include the military’s recent adoption of a new .277 caliber and the desire for longer-range shooting. As gun owners, we’re always looking for the next advancement in the tactical space, and many of us are just bored with the same old 5.56 cartridge.

Two incredibly popular alternative caliber options are .300 Blackout and .308 Winchester. Both fire .30-caliber bullets and both are rifle cartridges…but beyond that the differences between them are pretty vast. We’ll discuss the differences, how that impacts the uses of these cartridges, and how that can help guide your decision.

As a quick point of clarification, the .300 Blackout is also known as .300 AAC Blackout, .300 BLK, .300 BO, or most technically, 7.62x35. For the remainder of this article, we’ll refer to it as .300 Blackout, for simplicity’s sake. The .308 Winchester is more technically known as 7.62x51, and we’ll just call it .308 WIN. For now, let’s look at the .300 Blackout versus the .308 WIN.

Purpose 

The differences between .300 Blackout and .308 WIN are considerable. Let’s look at the provenance and purpose of these cartridges to better understand their respective roles. 

.300 Blackout

The .300 Blackout was designed expressly for use on the battlefield by special operators. Not only that, it was designed as a direct replacement for the 5.56x45 cartridge. The intent was to give the operator a .30-caliber bullet from the same AR-15/M4 platform; with minimal alteration and no change in magazine capacity. The .300 Blackout fulfilled this need perfectly. It functions in a standard AR/M4 platform, requiring only a change in the barrel. This yields a rifle with much more punch in close quarters.

The .300 Blackout also functions exceptionally well in short-barreled rifles. While the 5.56 loses significant velocity with every inch of reduced barrel length, the .300 Blackout is less affected by barrel length. While longer barrels can certainly increase velocity, short barrels of 8 to 11 inches still give an impressive performance. The .300 Blackout also suppresses exceptionally well and is capable of using both heavy, subsonic ammunition and lighter, faster, supersonic bullets driven at higher velocities. This allows the user to tailor the .300 Blackout to their needs. This exceptionally versatile cartridge can be a light-recoiling, short- to mid-range deer rifle, or suppressed to make it a formidable CQB platform.

.308 WIN

The .308 WIN is a very seasoned cartridge by comparison. At 71 years old, it is an old man compared to the teenaged .300 Blackout. The .308 WIN was designed as a full-power cartridge for use in battle rifles and machine guns. It was derived from the longer .30-06 cartridge that was fired from the M1 Garand. Improved powders generate higher pressures, allowing a cartridge with a shorter overall length to generate similar power. This also allowed the rifles that fired it to be smaller, as seen with the M14.

Today the .308 WIN is available in the AR-10 platform, making it basically a scaled-up AR-15 design. The .308 WIN has certainly proven its worth over the last seven decades. It has been a perennial bolt gun favorite of hunters. The .308 WIN has been the de facto chambering of military sniper rifles since the Vietnam War. It has also been the darling of the battlefield when fired through the M60, M240, and other medium, general-purpose machine guns where its power is perhaps most evident.

Let’s take a look at some of the other differences between these two cartridges.

Cartridge Size

The power differential between these two cartridges is a direct result of size.

The .300 Blackout is a stout but compact cartridge. It has a case length of just 34.7mm, hence the 7.26x35 designation. With an overall length of just 2.26 inches, it allows it to fit into a standard AR platform. It can share AR magazines and most AR parts, all as a direct result of its size. This also lowers its cost of entry, making it more accessible and less expensive than a .308 WIN build.

The .308 WIN is a much, much bigger cartridge. The case length is 51mm (compared to 34.7) but that doesn’t adequately tell the tale; it is also much larger in diameter. To look at the differences, let’s consider the case capacity. The .300 Blackout case will hold 26.5 grains of water. Comparing apples to apples, the .308 WIN case will hold 56.0 grains of water – over twice as much! This is why the .308 WIN requires a completely different platform from which to operate while the .300 Blackout does not.

Bullet Weight and Velocity

The .300 Blackout and .308 WIN also differ in their bullet weights and velocities.

The .300 Blackout fires bullets in the 110 to 220-grain range. The lighter bullets, up to around 180 grains, produce supersonic speeds, while bullets 200 grains and higher are generally subsonic. The very fact of being subsonic tells us something about velocity: the subsonic round will generally travel under 1,100 feet per second. This avoids a sonic “crack” when surpassing the sound barrier and makes suppressed shooting with subsonic ammo very quiet.

Supersonic ammunition from the .300 Blackout velocities differs depending on bullet weight and barrel length. From a 16-inch barrel, 125-grain supersonic rounds can be expected to deliver around 2,200 feet per second of muzzle velocity, with 110-grain bullets nearing 2,400 fps. There are some lighter, fast boutique bullets but 110- and 125-grain represent some of the most common loadings. 

The .308 WIN shoots a similar range of bullet weights, from 110 grains to 220 grains, with 150 to 180 being the most common. The velocity of a 150-grain bullet fired from a .308 will still leave the muzzle at 2,500 feet per second. That’s substantially faster than a comparable .300 Blackout bullet. It comes with additional kinetic energy as well, with approximately 1,200 ft-lbs of muzzle energy versus over 2,000. Again, that’s a big difference that comes into play for taking larger game, penetrating through barriers, etc.

Magazine Compatibility 

Everything in life is a trade-off. The additional power of the .308 WIN is no exception – it is a huge benefit but at a cost. That cost is magazine compatibility. The .300 Blackout uses standard, STANAG-pattern, AR-15 magazines. There are some magazines labeled specifically for the .300 Blackout, but it will use standard AR mags just fine. This prevents you from spending more money on magazines and lets you use the magazine wells you already own.

The .308 WIN, with its substantially larger size, requires its own magazines. There is a “standard” .308 WIN magazine that AR-10s use, but it’s far from being a universal standard. It also requires a larger receiver, which makes the gun both larger and heavier. Additionally, it has an impact on capacity; the smaller AR-15 magazines hold a standard capacity of 30 rounds. The larger .308 WIN magazines typically come with a 20-round capacity and they are quite large in comparison.

Range and Ballistics 

One huge difference between these two is the range.

As we have seen, the .300 Blackout produces less muzzle velocity and less energy than the .308 WIN. The .300 Blackout also generally comes in a shorter overall package, with 8- to 10-inch barrels being optimally suited to the smaller cartridge. This impacts velocity, as well, giving the .308 WIN an even bigger margin. Impacting velocity even further is the use of subsonic ammunition which is very heavy and travels very slowly.

The .308 WIN is a high-velocity cartridge that pushes all its standard offerings at supersonic speeds. It pushes bullets much faster, resulting in less bullet drop over long distances. As modern military sniper rifles have proven, the .308 WIN is capable of putting a bullet on a man-sized target at 1,000 yards all day long. The .308 WIN is the clear winner in this cartridge comparison when it comes to effective range and longer distances.

Deciding Which is Best for You

There are some pretty significant differences between these two cartridges. In the end, the choice boils down to use-case: what do you need the rifle to do? If you need a semi-automatic rifle for self-defense, with a shorter barrel, and possibly suppressed, the Blackout cartridge is probably the better choice. Loaded up with subsonic loads it would be a formidable home defense tool, and with supersonic ammo, it could easily flex into a hunting or ranch rifle.

The .308 WIN, on the other hand, is a powerful rifle cartridge with velocity, energy, and distance on its side. It can take game up to elk-sized, and though perhaps a bit overpowered for shorter ranges, can still function as a self-defense rifle. If you intend to shoot at longer ranges, the .308 is probably the better choice.

Regardless of which you choose (or if you choose both!), Ballistic Advantage has the parts for your next build, including complete AR308 uppers and uppers in .300 Blackout, and lowers for either cartridge, along with all the other parts and accessories you need.