6.5 Grendel vs 300 Blackout Ballistics & Uses – 2022 Comparison

The AR-15 platform has always been open to a lot of experimentation by wildcatters and mainstream manufacturers. Everybody wants to improve the platforms and innovations do seem to amaze. Everytime you think that the platform has reached its limit, there’s something new on the market. 

Two such additions to the greatness of this platform were the 6.5 Grendel and .300 blk cartridges. Designed to upgrade the effectiveness of the .223 Remington cartridge chambering of the AR-15, it seems like one of these stretches the legs, while the other widens the shoulders of the standard cartridge. 

Since both of them are an alternative replacement cartridge for the AR-15, this comparison will help you understand the pros and cons of each, and which one to choose. 

TL;DR: 6.5 Grendel vs 300 Blackout

A quick and simple table outlining the pros and cons of these rounds, and the summary of this comparison. Check it out for a brief overview of the topic.

6.5 Grendel

6.5 Grendel Round
Photo credit: rifleshootermag.com

300 Blackout

300BLK rounds
Photo credit: fedarm.com


6.5 Grendel

Ammo is quite inexpensive

Good penetration and stopping power

Versatile cartridge and very soft on recoil

Flat trajectory and good out to 800 yards

Capable of taking down big game animals at short range with the right loads

300 Blackout

Hard hitting power at short distances

Works great with suppressors and SBR

Capable of supersonic and subsonic functions

Achieves full potential in just nine inches of barrel length

Switching only needs a new barrel (and sometimes mags)


6.5 Grendel

Needs long barrel lengths

Doesn’t use an AR-15 bolt

Less ammo options and availability

300 Blackout

Not suitable for deer outside of 100 yards

Works only in short range. Not very flat-shooting

Best For

6.5 Grendel

What use/person is this product best for based on the relevant characteristics below?

300 Blackout

What use/person is this product best for based on the relevant characteristics below?

6.5 Grendel Overview

The 6.5 Grendel is a 6.5×39 mm cartridge developed collectively by Bill Alexander, Arne Brennan, and Lapua. The round was designed in 2003 and was intended to be a balanced round between the 5.56 and 7.62 NATO rounds. It was standardized by SAAMI in 2010 and entered commercial manufacturing for the civilian market. 

This round was designed to improve the power and range of a regular AR-15 rifle, and without creating any significant increase in recoil. The .308 Win (or 7.62 NATO) is a big and bulky round with a significant recoil and possible control issues for an average AR-15 user familiar with the .223/5.56 light-recoil cartridges. 

Photo credit: wikipedia.org

Another important factor that was taken into consideration was the compatibility of this cartridge with the standard STANAG magazines used with the AR-15/M4 setup. So a standard 30-round STANAG mag for the AR-15 holds 26 rounds of the 6.5 Grendel. The popularity of this cartridge was in stiff competition with the 6.8 SPC and 6.5 Creedmoor rounds, both of which were developed and released around the same time. 

In my opinion, the 6.5 Grendel is still a very unexplored cartridge by the shooting community, as many people prefer the 6.5 Creedmoor for long range versatility. However, the 6.5 Grendel still has its own very important place, which we’ll understand in the upcoming sections. 

300 Blackout Overview

The 300 AAC Blackout, also known as the .300 blk, or 7.62x35mm is an intermediate rifle cartridge developed by the Advanced Armament Corporation in the United States. It is a .30 caliber AR-15 round that was designed for the special forces of the military as an interchangeable cartridge for the 5.56 NATO ammunition. 

This cartridge can literally convert a 5.56 NATO chambered AR-15 into a .308 caliber rifle in under a minute. All that’s needed is to swipe the barrel, and even the magazine can be kept the same if it is suitable. In other words, the idea was to imitate the ballistics of a 7.62x39mm round in the same rifle chambered for a 5.56 NATO. 

Photo credit: wikipedia.org

As a matter of fact, the .300 blk is the only semi-automatic cartridge in existence today, that is can shoot subsonic and supersonic ammo without any changes. Additionally, this cartridge only needs nine inches of barrel length fto completely attain its potential, and it also works great with suppressors. It delivers even better performance than the subsonic 9mm rounds in a SBR.

Although this round was never adopted by the military, as it was intended to. However, the civilian population, and the AR-15 community took it with both hands and made it quite popular. 

6.5 Grendel vs 300 Blackout: Cartridge Specs

I’ve laid out a simple table comparing the dimensions of these cartridges for a quick overview. 

6.5 Grendel300 Blackout
Bullet Diameter0.264 in (6.71 mm)0.308 in (7.8 mm)
Neck Diameter0.293 in (7.44 mm)0.334 in (8.5 mm)
Base Diameter0.439 in (11.15 mm)0.376 in (9.6 mm)
Case Length1.52 in (38.7 mm)1.368 in (34.7 mm)
Overall Length2.26 in (57.5 mm)2.26 in (57 mm)
Case Capacity35 grains21 grains
Max Pressure (SAAMI)52,000 psi55,000 psi
Typical Casing MaterialBrassBrass
Typical Bullet Weight (gr)90-130 grains110-150 grains

The first and very obvious similarity between these two cartridges is the overall length, which is 2.26 inches and the same as a .223/5.56 AR-15 round. This is what allows all these three cartridges to use the same lower receiver, and also the same magazines. Other than this, the next bullet weights for these cartridges are also quite comparable and usually fall in the range of 100 to 150 grains. However, the .300 blk can use bullets as heavy as 220 grains for its subsonic ammo variants. 

The 6.5 Grendel uses a .220 Russian cartridge as parent case, which itself is a necked down version of the 7.62x39mm AK-47 round. It uses a slightly longer case compared to the .300 blk, but has slightly smaller bullets. The 6.5 Grendel uses a smaller 0.264 inch diameter bullet, compared to the .308 inch diameter bullet of the .300 blk. 

The 6.5 Grendel is also a slightly fatter case with a larger base diameter, because of its parent case. The .300 blk has the same base diameter as the .223/5.56 cases and hence uses the same bolt. The slightly longer and fatter case of the 6.5 Grendel allows it to store almost 50% more powder than the .300 blk. However, the .300 blk is loaded at a slightly higher chamber pressure to work out that supersonic-subsonic compatibility. 

Photo credit: projectgunner.com

6.5 Grendel vs 300 Blackout: Ballistics

The ballistics section will elaborate upon the values of trajectory, velocity and kinetic energy of these rounds over a set distance. These values will help us determine the accuracy, and effectiveness of different loads against various types of targets. 

For example, a round that shows a flat trajectory over a long distance will require lesser adjustments on the sighting setup and it will be suitable for long range shooting. Plus, if it also carries enough energy at long range, it can be used to engage different types of targets. 

6.5 Grendel vs 300 Blackout: Trajectory

Here is the data of trajectory for these cartridges, which has been determined using the most common and best ammo. 

6.5 Grendel

24” barrel/BC 0.264/90 grains
24” barrel/BC 0.506/123 grains
Hornady Custom SST
24” barrel/BC 0.570/130 grains
Federal OTM
100 yds: 0 “ Drop100 yds: 0 “ Drop100 yds: 0 “ Drop
200 yds: 3.5 “ Drop200 yds: 4.5 “ Drop200 yds: 5.4 “ Drop
300 yds: 13.5 “ Drop300 yds: 15.9 “ Drop300 yds: 18.5 “ Drop
400 yds: 32.1 “ Drop400 yds: 35.4 “ Drop400 yds: 40.6 “ Drop
500 yds: 62.3 “ Drop500 yds: 64.1 “ Drop500 yds: 72.9 “ Drop
1,000 yds: 564.1 “ Drop1,000 yds: 413.5 “ Drop1,000 yds: 450.5 “ Drop

300 blk

16” barrel/BC 0.290/110 grains
Hornady V-Max
9” barrel/BC 0.251/120 grains
Copper HP
16” barrel/BC 0.406/150 grains
FMJ Boat-Tail
100 yds: 0 “ Drop100 yds: 0 “ Drop100 yds: 0 “ Drop
200 yds: 6.5 “ Drop200 yds: 9.4 “ Drop200 yds: 10.3 “ Drop
300 yds: 23.4 “ Drop300 yds: 33.7 “ Drop300 yds: 34.7 “ Drop
400 yds: 54 “ Drop400 yds: 78.6 “ Drop400 yds: 76.9 “ Drop
500 yds: 102.7 “ Drop500 yds: 150.6 “ Drop500 yds: 140.2 “ Drop
1,000 yds: 806.3 “ Drop1,000 yds: 1075.6 “ Drop1,000 yds: 902.9 “ Drop

Before we start, you can see that the 6.5 Grendel has been shot using a 24 inch barrel, whereas, the .300 blk has been shot using shorter barrels and even a nine inch barrel. This has been done to determine the best shooting circumstance and also check the claims from the manufacturers. 

At any given point within 400 yards, the .300 blk will always have twice more drop than the 6.5 Grendel. Plus, beyond that 400 yard range, this difference starts to widen, and while the .300 blk shows an average drop of 950 inches at 1,000 yards, the 6.5 Grendel shows an average drop of 450 inches. 

Photo credit: militarytimes.com

So what does the .300 blk lack? Before you start seeing the .300 blk as an incompetent round in terms of trajectory, let me reiterate to you that it was designed for short range engagements. That too with a short barrel rifle and probably suppressors. The drop of a .300 blk is acceptable with 250-300 yard range, however, you’ll have to aim your rifle like a medieval front-row archer beyond that range. 

The 6.5 Grendel shows an impressive trajectory and drops just five feet at 500 yards. Looking at the case capacity and bullet weight, that seems good. While the .300 blk imitates the drop of a 7.62x39mm at 1,000 yards, the 6.5 Grendel does way better than that in comparison. However, the 6.5 Grendel still has a better trajectory than a .223 Rem at 1,000 yards, and similar trajectory to a .223 Rem out to 500 yards. 

6.5 Grendel vs 300 Blackout: Velocity & Kinetic Energy

Now let’s look upon the velocity and kinetic energy values for these rounds, out to a distance of 1,000 yards. 

6.5 Grendel

24” barrel/BC 0.264/90 grains
24” barrel/BC 0.506/123 grains
Hornady Custom SST
24” barrel/BC 0.570/130 grains
Federal OTM
100 yds: 2,647 ft/s, 1,400 ft.lbs100 yds: 2,409 ft/s, 1,585 ft.lbs100 yds: 2,254 ft/s, 1,466 ft.lbs
200 yds: 2,320 ft/s, 1,076 ft.lbs200 yds: 2,245 ft/s, 1,376 ft.lbs200 yds: 2,113 ft/s, 1,289 ft.lbs
300 yds: 2,017 ft/s, 813 ft.lbs300 yds: 2,086 ft/s, 1,189 ft.lbs300 yds: 1,977 ft/s, 1,128 ft.lbs
400 yds: 1,740 ft/s, 605 ft.lbs
400 yds: 1,935 ft/s, 1,023 ft.lbs
400 yds: 1,847 ft/s, 985 ft.lbs
500 yds: 1,493 ft/s, 445 ft.lbs500 yds: 1,791 ft/s, 876 ft.lbs500 yds: 1,723 ft/s, 856 ft.lbs
1,000 yds: 891 ft/s, 159 ft.lbs1,000 yds: 1,212 ft/s, 401 ft.lbs1,000 yds: 1,218 ft/s, 428 ft.lbs

300 blk

16” barrel/BC 0.290/110 grains
Hornady V-Max
9” barrel/BC 0.251/120 grains
Copper HP
16” barrel/BC 0.406/150 grains
FMJ Boat-Tail
100 yds: 2,094 ft/s, 1,071 ft.lbs100 yds: 1,799 ft/s, 863 ft.lbs100 yds: 1,724 ft/s, 990 ft.lbs
200 yds: 1,834 ft/s, 821 ft.lbs200 yds: 1,533 ft/s, 626 ft.lbs200 yds: 1,561 ft/s, 811 ft.lbs
300 yds: 1,597 ft/s, 623 ft.lbs300 yds: 1,307 ft/s, 455 ft.lbs300 yds: 1,411 ft/s, 663 ft.lbs
400 yds: 1,389 ft/s, 471 ft.lbs400 yds: 1,136 ft/s, 344 ft.lbs400 yds: 1,282 ft/s, 547 ft.lbs
500 yds: 1,218 ft/s, 362 ft.lbs500 yds: 1,024 ft/s, 279 ft.lbs500 yds: 1,174 ft/s, 459 ft.lbs
1000 yds: 846 ft/s, 175 ft.lbs1000 yds: 754 ft/s, 151 ft.lbs1000 yds: 896 ft/s, 268 ft.lbs

The data clearly points out that a .300 blk round loses its supersonic capability at 600 to 700 yards. That is with the normal supersonic loads, and I haven’t even recorded the data for subsonic loads. In comparison, the 6.5 Grendel has a better supersonic range with its medium and heavy loads that can extend out to 1,200 yards. 

The 0.264 inch diameter bullets of the 6.5 Grendel have a far higher ballistic coefficient, and coupled with their flat trajectory, these rounds will prove to be more accurate than the .300 blk. In comparison, the .300 blk has almost half the supersonic range, and which is totally fine because it is a short-to-medium range cartridge. 

Talking about the energy values, the 6.5 Grendel is way ahead than the .300 blk. For example, a 150 grain .300 blk round carries 990 fpe at 100 yards, but a 130 grain OTM 6.5 Grendel round carries 1,466 fpe at 100 yards. To give you an idea, it takes about 1,000 fpe to humanely (and legally) kill a deer, and about 1,500 fpe to kill a big game animal like an elk or moose. 

In fact the 123 grain rounds for the 6.5 Grendel can be used to effectively take down a big game animal within 100 to 150 yards. On the other hand, the .300 blk doesn’t even stand out as an effective deer hunting cartridge. Although, it does have a good amount of energy to kill varmints. Despite its big and heavy .308 inch diameter bullets, the .300 blk cannot outshine the 6.5 Grendel in terms of kinetic energy, as well as velocity. 

Like I already mentioned, the 6.5 Grendel was designed to perform somewhere midway between 5.56 NATO and 7.62 NATO. Interestingly, the 6.5 Grendel shows higher penetration and kinetic energy at 1,000 yards in comparison to the 7.62 NATO. 

6.5 Grendel vs 300 Blackout: Stopping Power

The best measure to understand the real-life effectiveness of a cartridge, is to understand its stopping power. Additionally, the two most definitive factors to evaluate the stopping power of a round are its momentum and sectional density. 

6.5 Grendel vs 300 Blackout: Momentum & Sectional Density

A table comparing the values of momentum for these rounds out to a distance of 1,000 yards.

6.5 Grendel

24” barrel/BC 0.264/90 grains
Sectional Density: 0.184
24” barrel/BC 0.506/123 grains
Hornady Custom SST
Sectional Density: 0.252
24” barrel/BC 0.570/130 grains
Federal OTM
Sectional Density: 0.266
100 yds: 34 lb.ft-s100 yds: 42 lb.ft-s100 yds: 41 lb.ft-s
200 yds: 29 lb.ft-s200 yds: 39 lb.ft-s200 yds: 39 lb.ft-s
300 yds: 25 lb.ft-s300 yds: 36 lb.ft-s300 yds: 36 lb.ft-s
400 yds: 22 lb.ft-s400 yds: 34 lb.ft-s400 yds: 34 lb.ft-s
500 yds: 19 lb.ft-s400 yds: 34 lb.ft-s500 yds: 31 lb.ft-s
1000 yds: 11 lb.ft-s1000 yds: 21 lb.ft-s1000 yds: 22 lb.ft-s

300 blk

16” barrel/BC 0.290/110 grains
Hornady V-Max
Sectional Density: 0.166
9” barrel/BC 0.251/120 grains
Copper HP
Sectional Density: 0.181
16” barrel/BC 0.406/150 grains
FMJ Boat-Tail
Sectional Density: 0.226
100 yds: 32 lb.ft-s100 yds: 30 lb.ft-s100 yds: 36 lb.ft-s
200 yds: 28 lb.ft-s200 yds: 26 lb.ft-s200 yds: 33 lb.ft-s
300 yds: 25 lb.ft-s300 yds: 22 lb.ft-s300 yds: 30 lb.ft-s
400 yds: 21 lb.ft-s400 yds: 19 lb.ft-s400 yds: 27 lb.ft-s
500 yds: 19 lb.ft-s500 yds: 17 lb.ft-s500 yds:  25 lb.ft-s
1000 yds: 13 lb.ft-s1000 yds: 11 lb.ft-s1000 yds: 14 lb.ft-s

The sectional density (SD) of an object is the ratio of its mass to its cross-sectional area. This value helps determine the penetration caused by an object. The concept is simple, the more mass is focused upon a smaller area, the more pressure it will create, which will translate to penetration. 

An SD value of 0.230 to 0.260 is considered optimal for medium game. Anything above that is good for big game animals, and anything less is suitable for small game animals. The 6.5 Grendel rounds show a better value of SD in comparable bullet weights because of their smaller diameter. The heavy 6.5 Grendel rounds are suitable for taking down big game animals. Additionally, the 6.5 Grendel has better armor piercing capability due to its smaller diameter and higher energy. 

The .300 blk bullets are suitable for hunting medium sized game at best. Although, they still offer enough penetration to defeat level IIIA body armor. 

The next definitive factor for stopping power is the momentum, which is the measure of the intensity of energy transfer from the moving bullet to the target. A higher momentum means more damage (larger wound channel) and vice versa. 

Since momentum is a product of mass and velocity, in comparable bullet weights, the 6.5 Grendel will always have higher momentum. So it will always have more stopping power at any range. However, the heavier .300 blk bullets, like the 220 gr subsonic have a higher BC, and a higher SD, but they still lack momentum. 

6.5 Grendel vs 300 Blackout: Use Cases & Effective Range

After looking through the data, let us now familiarize ourselves with the realistic expectations and applications for these rounds. 

Big Game Hunting

The 6.5 Grendel is a viable big game hunting round, especially when we are talking about elk and moose. Like our data showed, the round carries enough energy to kill an elk within 100 to 120 yards. The penetration of its bullets is appropriate and the momentum is just optimal. 

On the other hand, the .300 blk is definitely not a suitable choice for hunting big game. While you can find optimal sectional density with the heavy rounds, it simply doesn’t carry enough energy to handle big game. 

Medium and Small Game Hunting 

The 0.264 inch and 0.308-inch bullets have long been an inevitable choice for deer hunters.

Photo credit: gundigest.com

The 6.5 Grendel is a perfect deer hunting round, especially due to the fact that it can be fired from an AR-15. Obviously, there are many other options, but an AR-15 chambered in this cartridge instantly becomes very versatile for short or long range and for small or big game.

The .300 blk is suitable for deer with the right loads and only within a range of 100-120 yards. However, one thing the .300 blk is exceptionally good at is taking down hogs. So if you live in Texas or any other feral hog-infested areas, the .300 blk is a good bet against hogs of all sizes. 

Both these rounds are quite overkill for small game animals, and I’d suggest you get a .22 caliber round for that. 

Tactical and Military Applications

The .300 blk was designed for tactical applications, and it certainly presents itself as a viable candidate for such uses. However, the 6.5 grendel is also not far behind and has had a better military acceptance during its peak years. However, both these rounds didn’t get approved in the end. 

The 6.5 Grendel is a great alternative caliber to the 5.56 NATO on an AR-15 if you need power with long range effectiveness, but you will have to replace multiple parts. On the other hand, the .300 blk is great at interoperability and just needs a barrel replacement, but it is of little effect beyond 300 yards in tactical scenarios. Plus, it has almost twice the recoil and drop when compared to the 6.5 Grendel. 


The .300 blk is used in USPSA multi-gun competitions and delivers great performance for competitions. In my opinion, the 6.5 Grendel is a better alternative to the .300 blk because of its lower recoil and long range effectiveness. 

Home Defense

Since both these rounds are capable of penetration level IIIA body armor, I don’t think either of these will be suitable for home defense due to over-penetration issues. However, you can use either of these cartridges to protect your farm/ranch against predators. Additionally, I never recommend using rifles and rifle cartridges in urban settings for home defense. 

Photo credit: youtube.com

6.5 Grendel vs 300 Blackout: Costs, Availability, & Compatibility

Check out the costs, ease of customization, and other nitty-gritty info related to owning these cartridges. 

Fairly Priced and Available

The 6.5 Grendel and .300 blk have been around for more than a decade. While the .300 blk is in significant demand, the 6.5 Grendel does not have those kinds of numbers. Luckily, both these cartridges are priced similar and the .300 blk is available at a slightly cheaper and more versatile scale due to its higher demand. 

Both these rounds can be found at a price range of $1.5 to $4 per round. While the .300 blk has a number of bullet options and easy availability. The 6.5 Grendel has only four bullet weights to choose from. Plus, not every offline store carries them, so make sure you carry enough rounds on your hunting trip. 

Easy Customizability and Aftermarket Options

Since both these cartridges were designed for the AR-15 platform, they enjoy the ability to be heavily customized and coupled with an unending expanse of aftermarket upgrade options. While you need a different bolt, barrel, and mag for switching over to the 6.5 Grendel, you only need a barrel and mag to switch over to the .300 blk. 

Bottom Line

The 6.5 Grendel and .300 blk were designed to enhance the capability of the .223/5.56 AR-15/M4 platform without changing much with the rifle. The 6.5 Grendel uses a 0.264-inch diameter bullet that not only enhances the hitting power of an AR-15/M4 but also increases its effective range to about 800 yards. It is a very versatile cartridge capable of taking down small game, and also some long range accuracy in the right hands. 

The .300 blk uses a .308 inch diameter bullet and was designed for hard-hitting power in short to medium range engagements. This round can achieve its full potential in nine inches of barrel length, can shoot both subsonic and supersonic ammo, and works great with suppressors. This round is good for quickly converting your .223 AR-15 into a .308 AR-15, and handling varmints, and some medium game animals. 


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