6.5 Grendel vs .300 Blackout: A Complete Guide

Posted by Faxon Firearms Staff on Nov 10th 2022

6.5 Grendel vs .300 Blackout: A Complete Guide

6.5 Grendel and .300 Blackout are two of the most popular alternate calibers for the AR-15 and it seems like more and more shooters are turning to them for everything from hunting to home defense.

Let’s take a look at these two great calibers, see how they measure up to each other, which one is better in what areas, and figure out which one is the best for you.

6.5 Grendel and .300 Blackout: Similar Answers to the Same Problem

6.5 Grendel and .300 Blackout were both created to address more or less the same problem: 5.56 NATO can be underwhelming. Don’t get us wrong, it’s an extremely efficient round, but it lacks the punch and long-range performance of other rounds you can shoot in the AR-15 platform.

So much so in fact, that the US military (and probably NATO in general) will be moving away from 5.56 for main infantry rifles and SAWs. 6.5 Grendel and .300 Blackout were both created to improve on 5.56’s performance, while still being compatible with AR-15 rifles and existing mags.

They solve very different problems, however, and each excels in different areas leaving plenty of room for both of these awesome rounds to have a place in the pantheon of standard AR-15 calibers that shooters have to choose from.

Let’s take a look at what these rounds do well and how they compare.

.300 Blackout vs 6.5 Grendel

The short answer here is that .300 Blackout is designed to perform best at close ranges, especially out of short, suppressed barrels, and 6.5 Grendel was designed to carry more energy at longer ranges and has a better effect on flesh and blood targets overall.

This doesn’t really tell the full story though, so we’re going to compare them across a variety of categories to get a better picture of where exactly each round really excels, and where they might fall short to help you pick between the two.

Cartridge Specs

First, let’s take a look at some cartridge specs. Where relevant, all specs are taken from SAAMI guidelines at the time of writing, and are for comparison purposes for this discussion and not meant to be reloading or manufacturing info.

Max average pressure numbers are also assuming a 16” barrel and are from SAAMI. Case capacities are approximate and will vary depending on your brass, seating depth, and other factors.

.300 Blackout6.5 Grendel
Parent Case.223 Remington/.221 Fireball.220 Russian
Bullet Diameter7.62mm (.308in)6.5mm (.264in)
Case Length (SAAMI Min)34.75mm(1.368in)38.61mm (1.52in)
Overall Length (SAAMI Min)57mm (2.26 in)54.32mm (2.135in)
Base Diameter (SAAMI Min)9.601mm (.378in)11.2mm (.441in)
Case Capacity (approx)19.2gr35gr
Max Average Pressure (SAAMI Spec)55,000psi52,000psi

What we see here are two mostly similar rounds, though with different diameters, shoulder designs, and case capacities. Max pressures are similar, though obviously more capacity means more velocity and energy for the Grendel, which we’ll dive into more in the next section.

The other thing we’ll see is that both rounds use very common bullet sizes of .308 and 6.5mm respectively so there’s a huge number of projectile types to choose from for both, whether you’re buying off-the-shelf ammo or rolling your own.

One note for reloaders is that you do have a lot more flexibility with 6.5 Grendel in terms of powder just because of that extra case capacity, but you’re still going to be dealing with the same overall length (more or less).

Muzzle Velocity and Kinetic Energy

Now let’s look at velocity and energy at various shooting distances. All numbers are calculated based on an average of 10 of the most popular factory loadings on the market fired out of a 16” barrel, with projectile weights from around the middle of what is available for each round.

Again, there are no hard and fast numbers here, just rough averages, and your exact velocity and energy are going to vary based on everything from your rifle to your ammo to the humidity in the air. This is just for comparison’s sake.

.300 Blackout6.5 Grendel
Velocity (Muzzle)2,184fps2,591fps
Velocity (100 yards)1,968fps2,458fps
Velocity (200 yards1,734fps2,269fps
Velocity (300 yards)1,536fps2,095fps
Energy (Muzzle)1,313ft-lb1,818ft-lb
Energy (100 yards)1,036ft-lb1,585ft-lb
Energy (200 yards)810ft-lb1,377ft-lb
Energy (300 yards)609ft-lb1,191ft-lb

What we see here is that 6.5 Grendel not only leaves the barrel carrying more velocity and energy, but it maintains that energy much better and at longer ranges. At 200 yards, .300 Blackout is starting to fall under the commonly accepted minimum energy required for whitetail.

Meanwhile, 6.5 Grendel nearly has more energy and velocity at 300 yards than .300 Blackout does… at the muzzle. This results in a flatter trajectory and less drop due to air resistance and gravity with 6.5 Grendel as well.

This dramatic difference at hundreds of yards makes the 6.5 Grendel the clear winner ballistically. .300 Blackout starts to struggle immensely past 150 yards, by comparison, making its sweet spot close-in shooting, especially against game animals.

In close, however, the rounds are more similar. From the muzzle to 100 yards, both have more than enough energy to dispatch mid-sized soft targets, and .300 Blackout holds onto much of its initial velocity inside those ranges.

Still, Grendel starts faster and stays faster all the way out to the limits of these rounds' effective ranges, and overall experiences dramatically less trajectory degradation at a longer distance making it the clear winner here.


Recoil-wise, both rounds are so close that we really can’t claim that there’s a significant advantage one way or the other, but .300 BLK does have about 50% less recoil than 6.5 Grendel. Is it enough to matter? Not in any practical sense, no.

Still, if you’re after a very light shooting gun, .300 Blackout is noticeably lighter, especially with subsonic loads. If you’re looking for hard numbers, .300 BLK has about 4.02lbs of recoil energy and 6.5 Grendel has about 6.89lbs (which puts Grendel right in line with standard 5.56 ammo for comparison).

Practical Applications

Of course, spec sheets and numbers can only really tell you so much, so let’s take a look at some practical applications and see where these two rounds sit.


For hunting, things are a bit of a mixed bag and will depend on what you’re hunting and at what ranges.

For small to medium game like whitetail or feral hogs and at closer ranges, there’s really not much of a difference here. Past 150 yards or against larger game animals like elk, things start to diverge a bit and we see that 6.5 Grendel has a much better performance, and past 300 yards it’s no contest at all.

For sheer versatility and ability to take larger game at longer ranges, we have to give this one to 6.5 Grendel…with one exception.

If you’re hunting with a suppressor at close ranges, such as hunting hogs at night, then .300 BLK might be a better option because of the better-suppressed performance. Still, for anything larger than a whitetail, or anything further away than 150 yards, stick with Grendel.


For self-defense, unless you’re fighting off snipers, .300 Blackout is going to win this one in most other cases. AAC designed .300 BLK to work well at close ranges, out of shorter rifles (which are more maneuverable in close quarters).

All of this combines to make .300 BLK the better choice for defending the home and self-defense in general. 6.5 Grendel has more energy, yes, but not enough to justify the extra recoil and the longer barrel lengths required for complete powder burn.

The exception would be if you’re including defending livestock in your self-defense calculations, in which case 6.5 Grendel is going to be better at dispatching predators at longer ranges. It’s actually one of the best rounds for this purpose that you can fit in an AR-15 in fact.


For general recreation and shooting at the range, we have to give it to .300 Blackout. Most people are shooting at 100-yard ranges or less, and inside those distances, there’s not an appreciable difference between the two rounds for punching paper or ringing steel.

The general popularity of .300 BLK vs 6.5 Grendel, plus the economics of the cases and projectiles, means that .300 BLK is around 40% cheaper than 6.5 Grendel. This makes it a much more economical choice for simple plinking and fun at the range.

The exception would be if you’re doing any long-range shooting at hundreds of yards, where you will definitely notice a difference and see the benefits of the 6.5mm diameter bullet. Other than that. 300 BLK takes the cake here.

This leads us to our final comparison…

Price and Availability

This one has to go to .300 Blackout. While 6.5 Grendel is certainly available and a good value for what it does in the AR platform, the popularity and success of .300 Blackout plus the simple economics of the materials that go into the two rounds means that AAC’s baby is considerably cheaper and more widely available.

If you’re worried about your cost per round, especially if you don’t hand load, then .300 Blackout is the superior round.

Upgrade Your 6.5 Grendel or .300 Blackout Firearms with Faxon

Faxon Firearms has built a strong reputation among AR-15 builders as a reliable source of high-quality barrels, gas blocks, bolt carrier groups, receivers, and handguards.

We offer a variety of BCGs and barrels in 6.5 Grendel and .300 Blackout that allow shooters and rifle builders to swap easily from a 5.56 setup, or to build an entirely new rifle from scratch.

We also offer our own purpose-built, complete firearms to meet every need you may have for an AR-15-style rifle, be that hunting, home defense, competition, or just having a great time at the range.