Ultimate 300 Blackout Guide: Barrel Length & Build Tips

Hey there, fine shooter.

So I hear you’re planning on adding a rifle or pistol chambered in .300 Blackout to the collection, but you want to know what barrel length will best suit your needs.

And you may be asking yourself, “What is the best barrel length for .300 Blackout?”

Well, this question can easily be answered by asking yourself the following question: What are you planning on using it for?

.300 Blackout (I’ll often refer to it as .300 BLK, heads up) was developed for shorter barrels where a suppressor may be required and to match the energy that made the 7.62×39 legendary.

And it’s the most successful attempt at replacing the 5.56×45 cartridge. Since the 5.56 was developed around a 20-inch barrel, chopping inches off reduces ballistic performance drastically. But we’ll get into that more in a bit.

Let’s talk about some barrel lengths that may be right for your application.

Here’s a short list if you don’t have time to read this wonderfully written article.

Best Barrel Length Overall – 9 Inches

Best Barrel Length For Hunting – 16 Inch Barrel

Best Barrel Length For Subsonic – 7 Inches

Best Barrel Length For .300 Blackout Pistols – 6 Inches

The 9 and 6-inch barrel lengths are what I recommended for those looking for a home defense gun in .300 Blackout.

Best Barrel Length Overall – 9 Inch Barrel

Ballistic Advantage 9” .300 Blackout Barrel

Pros & Cons

Before I get into this, the best barrel length for .300 Blackout all depends on how you plan to use your gun. But from a ballistic standpoint, 9 inches is where things start to get good.

When Advanced Armament Company developed the .300 Blackout cartridge, it was their understanding that the 9-inch barrel was the optimal length to get a full powder burn and get the most out of the round.  

The idea was to deliver big stopping power in a barrel length that would not dampen the ability to move in and around corners or tight spaces. Which is why .300 Blackout is in use by many Special Forces personnel in the U.S. and U.K.

And I’m sure you’re here because you’re trying to find out what barrel length to use on your SBR or AR-Pistol. So, 9 inches is your answer. You can go lower, but nothing lower than 6 inches.

Note: The 9-inch barrel length is pretty much the best barrel best length in all situations. Obviously.

Whether you’re planning on shooting suppressed or unsuppressed, subsonic or supersonic loads, or using .300 Blackout for home defense.

The 9-inch barrel is also one of my recommendations for home defense.

Best Barrel Length For Hunting – 16 Inch Barrel

Ballistic Advantage 16” .300 BLK Barrel

Pros & Cons

I recently opened up my YouTube to find a video of a gentleman and his brother hunting hogs.

They crept up closer and closer, set down their tripod, and took aim.

Four hogs sit grazing on the land. Totally unaware that one of them just gnawed on the earth for the last time.

Seconds later, the hog drops. And the rest scatter away. After a few seconds of kicking, the hog was Sayonara.

.300 Blackout = 1

Hog = 0

And that doesn’t include the other videos I saw of hogs being mowed down by gentlemen on the back of a Polaris. Or on a helicopter hurling .30 caliber rounds on some unsuspecting hogs eating the crops.

Bye-bye, back to the lobby.

Sorry, those videos got me pumped up.

Anyway, even though .300 Blackout was made for shorter barrels, it does one hell of a job from the 16-inch barrel when paired with supersonic rounds and a 1×8 magnification scope.

For a clean and honest kill, I wouldn’t recommend hunting with subsonic rounds. Just keep it supersonic, and you can get the job done easily.

Best Barrel Length For Subsonic Ammo – 7 Inch Barrel

Faxon Firearms 7.5” 300 BLK Barrel

Pros & Cons

If you don’t know what subsonic means, sub-rounds fly under the sound barrier and get rid of that supersonic “crack.”

They are usually heavier than supersonic rounds. Which makes them great up close. I would only use them up close, though. At a distance, they lack in performance.

Anyway, we’ve established that .300 Blackout does best in shorter barrels. So we have that out of the way.

And since most folks want subsonic ammo to run in their suppressor, we can chop an inch off of the barrel and let the suppressor make up for it.

With an overall length of 13 inches, you still have all of the benefits of the longer 9-inch barrel while still leaving room to suppress the rifle (or pistol).

And if you’re looking for a truck gun or home defense gun that can be deployed easily or stowed into a backpack for SHTF scenarios, the 7-inch barrel will fit in just fine. With and without the suppressor.

Mind you, an 8 or 9-inch barrel will also do the trick if you want a bit more muzzle velocity from your rifle or pistol.

Best Barrel Length For .300 Blackout AR-Pistols – 6 Inch Barrel

Faxon Firearms 6” 300 BLK Barrel

Pros & Cons

The 6-inch barrel is the shortest you can get before you start to lose out on the .300 Blackout cartridge. And since we’re talking about AR-Pistols, why not go with a 6-inch barrel?

Matched with a suppressor and some subsonic rounds, you can tuck this little AR-Pistol in a backpack or in the truck if you ever need to get home quietly.

And, in some states, it is perfectly legal for you to have an AR-Pistol in your car. If t isn’t legal, you should probably move out of there. Trust me, having an AR-Pistol chambered in .300 Blackout is worth it.

This is where we start to see the genius behind the .300 Blackout round.

Not only do you have a round that can deliver 1,000 ft pounds of kinetic energy to the target, but it’s quiet, works in shorter barrels, and you never have to worry about pulling the trigger twice.

This barrel length is also another one of my recommendations for home defense.

Even Nelson Mandela kept his ear on the streets, and I’ve learned everything I know by asking questions. Luckily for me, I have a bunch of friends who not only sell guns but shoot them as well. And they always have something new to show me when I ask my questions.

So, as usual, I went to my local gun range and talked to the boys. Most of them have .300 Blackout builds and have been involved in gunsmithing for years.

Doing some research before sealing the deal on your barrel is always a wise thing to do. After all, you don’t want to end up with the wrong thing, do you?

What Are You Using It For?

This is always the most important thing to ask yourself before buying anything in the gun world. Since the gun world can be expensive, buying the wrong barrel length can be disappointing and costly.

So, please, before buying your barrel, consider what you are planning on using it for.

If you want to use .300 Blackout for home defense, you wouldn’t buy a 16-inch barrel, would you?

Likewise, if you want to use your .300 Blackout build for hunting, buying a 7-inch barrel might not be the smartest thing to do.

As a rule of thumb, I recommend the 9-inch barrel to anyone who is looking into building a rifle or pistol chambered in .300 Blackout. Unless you know exactly what you need.

Home Defense With .300 Blackout

Now I’m not trying to take a leak in anyone’s punch bowl, but if you’re looking into .300 Blackout for home defense, there are some things you need to consider before making it your go-to home defense round.

One, where do you live?

You’d be surprised how many people who live in apartments in close proximity to their neighbors use 5.56 or .300 Blackout for home defense. Which, excuse my hostility, is one of the most idiotic things you can do as a responsible gun owner.

But I’ll help you clear that up.

Consider the walls in your dwelling. And look at the outside to see what your apartment/house is made of. If you have sheetrock walls and vinyl siding, you might be in for a world of trouble if you shoot an intruder, through the wall, and into the head of the little kid sleeping in their bed.

I know, sounds graphic, right? Let’s avoid that.

On the other hand, if you live in a house with vast land all around. The only thing you have to consider is the people inside your home. This is where the backdrop comes in.

Backdrop, fine shooter. Backdrop… What is a backdrop?

Put simply, it’s better to drop a target standing in front of a brick wall than in front of a school. Are you picking up what I’m putting down?

So, if you live in a home with a wife and kids, cutting off the intruder as quickly as possible is important. Or, at the very least, take away his/her ability to be in the same vicinity as the room where your loved ones are staying.

To sum it all up, if you live in an apartment or in close proximity to neighbors, don’t use a rifle cartridge like .300 Blackout or 5.56 for home defense. If you live in a house with wide open land, send it, and just make sure you know what’s beyond your target.

Fine shooter, you hear? ALWAYS know what is BEYOND your target.

While .300 Blackout didn’t exactly accomplish its purpose of replacing the 5.56 cartridge, it is one of the most promising rounds that have been introduced to this day. It’s perfect for close-quarters engagements and under the cloak of a suppressor.

Once you match that suppressor with a 9-inch barrel and some subsonic rounds, the end result is a close-quarters combat machine.

For all intents and purposes, the 9-inch barrel length is perfect for .300 Blackout. Whether you need a home defense gun or a truck gun, you can’t go wrong here.

Anyway, thank you for taking the time to read. If you have any rifles or pistols in .300 Blackout, leave a comment below and let us know what barrel length you have and why you love it.

I love you.

See you on the range, fine shooter.