How To Convert AR15 To 300 Blackout

This guide goes over how to convert AR15 to 300 Blackout, regarding barrel specs, and clarification on which BCG to use.

The .300 Blackout is a highly effective round that bridges the gap between the popular 223 and 7.62 rounds. And yes, converting a 223 or 5.56 AR15 to a 300 Blackout chamber barrel is very straightforward.

Users can simply swap out the entire upper receiver or just swap the barrel. Here are some details to note:

300 Blackout Specs

The .300 Blackout, formally standardized by SAAMI in 2011, was developed by the Advanced Armament Corporation (AAC) in collaboration with Remington Defense.

It was designed to meet a set of specific needs, including compatibility with:

• Existing AR-style magazines while maintaining the same magazine capacity
• Utilizing M4-style platform uppers and lowers
• It uses the same bolt carrier group as 5.56 NATO AR15
• Optimized for suppressor use when using subsonic ammo
• Ballistic performance similar to the 7.62mm x 39mm round

Additionally, it needed to be a high-mass barrier-penetrating bullet while still providing low recoil and high performance in short-barreled, suppressed configurations.

Changing The Existing AR15 Upper Receiver

Popular BCM 300 Blackout Upper 9"

The easiest way to convert an existing AR15 into a 300 Blackout AR15 is to swap the entire upper receiver. There are many pre built 300 blackout upper receiver on the market.

While the 300 Blackout performs the best with a 9" barrel along with suppressor use. Many AR15 pistol uppers chambered in 300 Blackout are popular. 

If not, then go with the 16" barrel. (Remember, pistol AR15 receiver goes with short barrel uppers ONLY)

Swapping The Barrel To 300 Blackout

If you are not interested in buying a complete 300 Blackout upper receiver, the second method is to buy a 300 Blackout barrel and put it on your existing upper receiver.

Converting an AR-15 chambered in .223/5.56 to .300 Blackout is relatively straightforward, often requiring only a barrel swap. Although some other components may need to be changed, the process primarily revolves around removing the .223 barrel and installing a .300 Blackout barrel.

Specialized armorer tools, such as an armorer's wrench and a punch set, may be necessary for the conversion process. Consideration can also be given to a complete armorer's kit, which provides a comprehensive set of tools for various AR-15 modifications.

This method is ONLY easy if you have all the tools and a workbench required to do the job. 

Uses The Same AR15 Magazine

300 Blackout AR15s use the same magazine that can hold 5.56 rounds. Yes companies now do make 300 Blackout specific magazines with "300 Blackout" markings on it.

300 Blackout Ammo Availability 

The availability of .300 Blackout ammunition may vary, with supersonic options being more readily found in stores like Walmart compared to subsonic rounds.

However, subsonic .300 Blackout ammunition can generally be found in most gun stores and big box sporting goods stores.

While the price range for supersonic .300 Blackout ammo varies significantly, with options ranging from $16 to nearly $50 for a box of 20 rounds, subsonic rounds typically range from $20 to $25, with fewer choices available.

So as far as high volume shooting training goes, 300 Blackout is still not financially viable compared to the popular 5.56