What is a .300 Black out Upper?
What is a .300 Black out Upper?

The AR platform is one of the most diverse platforms in firearms manufacturing history. Since the early days of American gunsmithing, the popularity of interchangeable parts has skyrocketed, and culminated in the modern AR-15. The .300 blackout upper, which is a variation of the standard AR-15, is an upper assembly chambered for the .300 AAC Blackout caliber. It features the same design for the gas system, and works effectively with the standard AR-15 bolt carrier group. So what’s all the talk about the .300 blackout upper?

The .300 blackout caliber

The .300 blk is a rimless cartridge  bottlenecked cartridge with a bullet diameter of .308 in, or 7..62 mm. That puts it’s bullet weight on the same tier as the .308 Winchester and the 7.62×51 and other related calibers. It was developed in the United States by the Advanced Armament Company, hence why it is called the .300 AAC Blackout. It’s main purpose: to see use in the military as the standard cartridge for the M1 Carbine. 

The .300 AAC blk has seen use in both the military and commercial market, as a favored round among American hunters. Although it’s effective range is not as high as most traditional hunting calibers, the cartridge is designed to be used in conjunction with suppressors. It has a high velocity, but does not have the range capabilities that other hunting cartridges do. It is a versatile cartridge that is great in many situations.

.300 blackout and suppressors

The .300 blk caliber was originally designed to be used with suppressors. The super sonic and subsonic variants of the cartridge are perfect for suppressing the sound of the muzzle blast, making it ideal for hunting, target shooting, and much more. 

 .300 blackout pistol Uppers

The .300 blackout  is made for use in pistol uppers, with optimal barrel lengths being under 10” excluding the length of a suppressor. The .300 black out does not have as much charge in it as other cartridges of the same caliber, which means that it can be more effective in .300 black out uppers with shorter barrel lengths. The .300 blackout works great in AR pistols.

.300 Blackout upper Gas system

The gas system of the .300 blackout is similar to the one in the standard AR-15, but is different in a few key aspects. It is possible to run a AR-15 pistol kit gas system (gas tube and gas block) with the .300 black out, but in order to maximize the durability of your gas system, it is imperative to use a gas system made for the .300 blackout specifically.  The .300 black out has a much higher pressure than the .223 and will cause your gas system to wear much quicker if not handled properly. 

.300 black out upper gas systems are essentially adjustable gas blocks with a quality gas tube. The gas block must be adjustable because the different settings are meant to accommodate the varying pressures of the different kinds of .300 blk cartridges. Especially when using a .300 blk upper equipped with a suppressor, the gas block will need to be set specifically to maximize its efficiency.

.300 Black out Upper Vs AR-15 Upper

There are not very many differences when it comes to the AR-15 upper and the .300 blackout upper. The main differences are in the upper, while the lower of the AR-15 and the .300 blackout kit are exactly the same. The .300 blackout upper uses a different barrel and gas block, essentially making the two firearms interchangeable to one lower. Even the upper receivers on the two uppers are interchangeable, however constant disassembly is not recommended in order to switch from .300 Blackout to .223/5.56.

The .300 blackout was made in response to a desire that the .223/5.56 could not fulfill. However, it was intentionally made to fit into the same magazines, bolts, and other components to the AR-15 that are interchangeable between the two firearms. 

A 125 gr .300 blackout is capable of speeds up to 2,215 ft/s while a 55 gr .223 is capable of reaching 3,240 ft/s. You might think that is a bad thing, but in fact, much of the energy transferred to the speed of the projectile is used by its mass, doubling the amount of muzzle energy that a .223 would have. It is capable of a higher amount of damage although at a shorter range than the .223/5.56.

Why Buy a .300 blackout upper?

.300 blackout has become a very expensive round recently. The ammo shortage of 2020 has driven the price up and it has remained consistently high since then. However, that does not make the.300 blk inferior to the .223 which is also much more expensive than it used to be. Out of a suppressor, the .300 blk is capable of driving more power than the standard .223 and a .300 blk upper upper is capable of using the same lower. Essentially, if you have a standard AR-15 build, you would only need to buy a .300 black out upper in order to have a fully functioning .300 blk AR.

The .300 blk is a versatile round. It is capable of delivering high energy at medium ranges and is suitable and specialized for suppressors. The uppers are inexpensive and reliable. Buying a .300 blk upper is an investment that gets you two guns for the price of one if you have an AR-15 lower already. At Steel Fox Firearms we prize quality, customer service and the desire to see all of our customers with the guns they want. Purchase on our website or come find us at our storefront location.


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