300 BLK has a max pressure loaded lower than 5.56, extractors last about the same, use a good quality mil spec extractor ,bolt, and spring set up and you will have no issues.

 

Sons of Liberty Gun Works 5.56 M16 / AR-15 Bolt Carrier Group - Phosphate

If you are looking to build an AR-15 for hard use, to standards that exceed Mil-Spec expectations, then look no further than Sons of Liberty Gun Works.

www.primaryarms.com

this is a great BCG and will give years of trouble free service

 

you can get the same BCG but a bit cheaper if you just buy an unmarked microbest BCG instead of the SOLGW marked model

 

300 uses a 5.56 bolt, so you should see similar life from any (quality) extractor.

 

Another nice one is here ($99.99 +free ship)
Probably the best BCG deal around right now.

Toolcraft Logo'd Premium 5.56 Nickel Boron BCG with Carpenter 158 Bolt - 5165449729

Manufacturer: Palmetto State ArmoryProduct Line: ToolcraftPlatform: AR-15Includes: Premium BCGFinish: Nickel Boron

palmettostatearmory.com

Toolcraft Non-Logoed Premium 5.56 Nickel Boron BCG with Carpenter 158 Bolt

Manufacturer: ToolcraftPlatform: AR-15Includes: Premium BCGFinish: Nickel Boron

palmettostatearmory.com

 

Another nice one is here ($99.99)

Toolcraft Logo'd Premium 5.56 Nickel Boron BCG with Carpenter 158 Bolt - 5165449729

Manufacturer: Palmetto State ArmoryProduct Line: ToolcraftPlatform: AR-15Includes: Premium BCGFinish: Nickel Boron

palmettostatearmory.com

Toolcraft Non-Logoed Premium 5.56 Nickel Boron BCG with Carpenter 158 Bolt

Manufacturer: ToolcraftPlatform: AR-15Includes: Premium BCGFinish: Nickel Boron

palmettostatearmory.com

Lately, there has been a lot of bad press about NiB BCG’s. Not sure I’d run one over a standard

If you’re gonna run NiB, you should atleast do some searches of M4 carbine or Arf com and make a informed decision.

 

I'd buy Toolcraft with confidence.
Their CS is top notch if anything went awry.

 

I picked up a few Toolcraft BCGs ahead of time and they've been just as dependable as any other BCG I've ran; I'll probably use one for this build as well. I personally prefer the phosphate treated and chrome lined gas key/bolt channel in the carrier setup based on opinions from SOTAR and others. Never had a problem with NiB but all I've used are Failzero BCGs. Of course FZ has their issues with gas key screws and staking but that's something immediately fixed by sending them back with a set of OCKS on their dime.

 

The ONLY thing that I've seen break on an AR-15 in years of competitive shooting was a charging handle. The charging handle on a friend's rifle had the end break off opposite the latch lever (forward end of the lever). One of the guys loaned him the part and he finished the match. I keep a spare charging handle in my spare parts kit.

How about buying a spare extractor to keep in the handle cavity of your new lower? The easiest way would be to stash an entire bolt assembly. They're not expensive and easy to install. The bolt for a .300 Blackout is the same as a 5.56 bolt.

Flash

 

The only problem I had with a 10.5 inch barrel on a 300 blackout was with cases not extracting while shooting suppressed. The extractor wouldn't stay engaged on the rim. I used the BCM o ring under the extractor spring and it worked fine.

 

That's a heavily overgassed pistol, to be expected when attaching a suppressor. I had the same issue with suppressing my AR10, but I couldn't swap the extractor spring because of the proprietary setup. Ended up switching to a heavier buffer to fix that issue but in your situation I personally would've used a colt gold extractor spring or sprinco 5 coil no o-ring.

 

I looked up the bolt assembly at Midway. With the sealing rings and the extractor and ejector assembled, you can get one for $40. The .300 Blackout uses the same lower part of the cartridge case as the 5.56, so the bolts are the same. Replacing the bolt assembly is easy!

Get a handle with a trap door and carry it with you all the time.

Flash