With substantially more stopping power than 5.56, the .300 BLK has become an immensely popular cartridge for defensive applications, especially since it is light, similar in size, and produces similarly low recoil.
Add onto that the fact that you can resize 5.56 cartridges to load your own .300 BLK and that you can use a lot of the same parts from a 5.56 AR, and you have a winning combo.
In fact, you may be able to use all of the same parts except for basically just the barrel - which makes a conversion easy.
So, whether you’re reconfiguring an existing rifle or building a new .300 BLK from the ground up, here’s how to plan for success.
The .300 BLK Upper
Since you can reuse most of the same parts from a 5.56 rifle, as well as the same lower, you don’t need to pay that any more. You can use what you’re used to, though you might want to give the trigger and the buffer weight some thought.
Anyway, the upper is where you’ll need to turn your attention, specifically the barrel and handguard. If you’re building with a .300 BLK upper and the purpose is defensive, then consider a shorter option, specifically a 16” upper, for a few reasons.
The first is maneuverability. A 16-inch .300 BLK upper will weigh substantially less than a longer one, making it lighter and easier to handle, especially in tight spaces, which is where you might be called on to use it anyway.
The other reason is there really is no merit to going with a longer barrel like an 18” or 20” version. In fact, almost all .300 BLK uppers are 16” or shorter, and many are designed for building AR pistols. There are few that are longer because all the benefits of a longer barrel are lost here.
In addition to the fact that they are heavier and harder to handle, the other main benefit of a longer barrel is the stability that engenders greater accuracy at extended accuracy. With a .300 BLK rifle, this really offers no value. This cartridge is not very useful beyond 100 yards anyway, making the longer barrel a waste.
The other consideration you’ll want to make with the upper is what type of handguard you want to go with. Your main three options will be Picatinny, KeyMod, and M-LOK rail systems.
The Picatinny rail system is the classic and has been in use for several decades. There are countless attachments made for Picatinny rails and they are proven and reliable. The thing is, they are heavy and uncomfortable to use without gloves, although they do offer a solid grip.
Both KeyMod and M-LOK rail systems, though fairly expensive, are much lighter than Picatinny rails, and every year there are more and more shooting attachments produced for them. So, ultimately the choice is yours here. Unlike barrel length, in which shorter is better for a .300 BLK, your choice of rail system is really a matter of preference.
Attachments and Accessories
Once you’ve chosen a .300 BLK upper and built the rifle, you can customize it to your intended shooting discipline with purpose-chosen attachments. Here are some of the best attachments you can use to improve the utility and serviceability of your .300 BLK rifle.
- 1-point sling: While this is not 100% necessary, many builders find that a 1-point sling is better for defensive applications than a 2-point sling. A 1-point sling improves retention. If your rifle ever jams, fails to fire, or you run the mag dry, you can release the rifle and draw a sidearm. This is the only purpose of the 1-point sling, so if you do build a rifle with one make sure you include sling mounts, which are affordable and easy to install.
- Flash hider or muzzle brake: Either one of these muzzle devices makes sense on a rifle destined for defensive use. The flash hider helps divert the muzzle flash from the shooter, preventing the flash from obstructing the sight picture and temporarily blinding the shooter. As for the muzzle brake, it performs a similar function with the added benefit of substantially reducing felt recoil. Not that this is a particular problem with a .300 BLK, but every little bit counts. The less felt recoil the rifle produces, the more it will combat muzzle flip, which will keep your sights on target for faster, more accurate follow up shots.
- WML: There is a saying in some circles, what you can’t see can kill you, and it refers to threats that move about under the cover of darkness. Tacking a WML, or weapon-mounted light, onto your forend via the rail system will give you the power of light at the tips of your fingers, so you can illuminate and identify, or even startle a threat, with the push of a button.
- Red dot sight: When it comes to .300 BLK as a caliber, there’s really no use for a scope. Scopes should be reserved for intermediate and long range shooting, both of which are not ideally suited for the .300 BLK. Expect to engage targets at close ranges with this caliber, which makes a scope fairly impractical. Instead, opt for a red dot sight that will enable you to keep your sight picture clear and unobstructed, and which will allow for faster target acquisition, will be parallax free, and will work in the dark. Alternatives to red dots in this scenario include reflex sights and holographic sights.
- Offset, backup iron sights: Never forego the offset-backup sights. A good pair of backup iron sights are a lifesaver if the battery dies in your main optic. Plus, these AR15 sights can be deployed easily, are affordable, and are shockproof, dustproof, waterproof, and so on and so forth. They also work in any conditions (including the dark) and keep you compliant with the maxim “two is one and one is none.”
- Folding vert grip: Some shooters feel that having a vertical grip on the rifle’s forend gives better control and affords superior, faster, more responsive handling, especially at close ranges. Get one that you can fold up against the forend so you can decide when and where you want to utilize it.
Getting Started with a .300 BLK Upper
If you’re considering building the ultimate .300 Blackout rifle, start with a .300 BLK upper from us. We sell .300 BLK uppers for both carbine-length and pistol-sized ARs, as well as other AR15 pistol uppers, along with all of the parts and shooting accessories you need to complete and customize a practical build.