The 300 Blackout AR15 uses the same 5.56 BCG. No extractor difference either.
If you already possess a 5.56 NATO platform and want to shoot the 300 Blackout, you can simply acquire a 300 Blackout barrel without the need for separate bolt carrier groups or charging handles.
This makes converting a 5.56 AR15 to 300 Blackout rifle super simple and straightforward.
This cost-effective approach enables shooters to enjoy the benefits of both cartridges while minimizing additional investments in firearm components.
This is a cost effective AR15 BCG from PSA that we highly recommend to try if you are converting a 5.56 rifle to a 300 Blackout on your primary upper or on a spare receiver.
The 5.56 and 300 blackout both have the same base diameter dimension for the bolt carrier group to work. When it comes to performance, the weight of the BCG and the coating of the BCG matter a little bit more when shooting the 300 BLK either suppressed or unsuppressed.
Most bolt carrier group on the market are full auto rated to work with a full auto and semi auto lower.
The best BCG to get by standard are ones with the following specs:
Quality Bolt Carrier Group Standards
Common malfunctions are centered around failures to extract or eject. One of the most common causes of short-stroke malfunction is a leaky gas key. This can be because a fastener has broken in there, or a fastener has backed out.
While most 300 Blackout BCG on the market today are meeting the standard, these are bare minimum specs any bolt carrier group should have in either a full mass or variable mass.
Bolt Carrier Group Weight
A full mass carrier is extremely reliable and offers more mass regulation. It's a great option if you're not running an adjustable gas block. If you're planning on running a suppressor on the rifle, this carrier provides the additional mass you need in the system.
A variable mass carrier offers additional reliability with its ring weights on the tail end. These ring weights provide a buffering effect to remove bolt bounce and help get past carbon fouling or other debris that might slow the bolt carrier down.
Adjustable Bolt Carrier Group For Shooting 300 Blackout Suppressed
(Assuming 9" 300 blackout barrel with adequate gas port size 0.070 inches)
300 Blackout is a versatile cartridge that can be fired both supersonic and subsonic. Since subsonic rounds require more gas pressure to cycle the action reliably, proper gas regulation becomes paramount.
Adjustable gas blocks and piston systems offer additional control over gas flow and can help fine-tune the firearm's cycling for both supersonic and subsonic loads.
High Pressure Tested (HPT)
HPT, or high pressure testing, is done to make sure that the bolt can handle high chamber pressures and keep firing without any risk of failure. In this test, the BCG is used to fire with a high pressure cartridge that is well over the SAMI specifications. The bolt is then MPI tested to make sure that the high pressure round doesn't do any damage to the steel.
In addition, 158 carpenter steel bolts that have been individually HP tested are reliable. Nickel boron is not recommended as a finish due to issues with cleaning and potential weakening of the material.
Magnetic Particle Inspected (MPI)
MPI, or magnetic particle inspected, is a quality testing process which allows the manufacturer to make sure that there aren't any microscopic cracks in the surface of the BCG. The BCG to be tested is placed on a magnetic field and a liquid solution containing magnetic particles is applied to its surface.
If there are any cracks or imperfections in the surface of the BCG, the magnetic particles stick to them. Ultraviolet light is then used to illuminate the imperfections, making them visible. So bolts that are MPI tested have lower chances of surface cracks and damage.
Shot peening is a process used to make metals more stress resistant. It is commonly used in engine pistons, however, it can also be used to make the bolt carrier groups for an AR-15 more durable and long-lasting.
Staked Gas Key
Lastly, the gas key is an important part of the bolt carrier group. It takes the full impact of the gases returning from the gas tube, therefore it needs to be properly fit into the BCG. Normally two screws are used to mount the gas key to the bolt carrier.
In a properly staked gas key, the metal on the sides of the screws is bent and staked into the screws to prevent them from backing out.