Back to the fun stuff: 300 BLK SBR Project

Exciting news at Mission Control: I was able to purchase a 9″ AAC upper receiver and have it in hand. Today it remains a pistol (translate: no stock, just a naked pistol buffer tube is what sets a pistol lower apart from a standard AR lower) but eventually my paperwork will be complete on an SBR lower receiver. At that point I will be able to combine the lower receiver I am building with the upper receiver to create a beautiful creature similar to the one pictured above. 

 The 300 Blackout packs a lot of punch out of a compact package (earlier ravings about all the utility and innovation of the BLK if you’re curious)

  • 25% more muzzle energy from a 9″ 300 BLK barrel than a 5.56 from a 9″ barrel
  • 300 BLK has a flatter trajectory than 5.56 NATO- a big problem with 5.56 out of short barrels is that projectiles tend to tumble very quickly (thus accuracy suffers)
  • The 300 BLK was designed to run supersonic and suppressed subsonic without gas system adjustments 
  • The 300 BLK is a very efficient cartridge- it doesn’t need much powder and doesn’t create much muzzle flash. That makes powder go further if you load your own ammo-which sounds pretty good these days.

To add to the last point above- if you are running a rifle like this you really owe it to yourself and anyone around you to add a can (a suppressor, aka silencer). It further reduces muzzle flash and really softens the concussion from the muzzle. That helps not only you but also your compadres since the people around you catch most of the muzzle concussion. Good news btw- Advanced Armament makes a 7.62 can that was designed to compliment the 300 Blackout – the coveted AAC 762-SDN-6

First impressions on the upper

The KAC URXIII free float rail and forearm system is impressive. Knights Armament did a good job keeping it lightweight. The aluminum hand grip area is really comfortable. I cant wait to put some rounds through it- there is a very natural feel to the upper.

I ordered some furniture from Knights to help facilitate a C-clamp front hand grip- they offer a panel kit. The panel kit basically accomplishes what the Magpul AFG seeks to accomplish- a support for your hand that facilitates a nice, natural C (like Chris Costa is demonstrating in the photos and videos here).The Knights panels are nearly the same price as an AFG and fit this kit perfectly. Either product is far superior to the pistol grip or mini pistol grip as far as I’m concerned.

Even in a pistol lower receiver the AAC upper has a natural feel to it. The charging handle is solid- no worries about bending this baby like some of the entry-level builds and kits do. I will add an extended latch to the charging handle though. Sadly that’s all I can tell you for the moment.

What’s next to keep the build rolling?

I decided to go with a co-witness sighting approach. That means flip-up “iron sights” with a compact red-dot type 1 optic in the center. You only need to use the rear flip-up if the dot fails. Not only is it cheaper than an EOtech or ACOG, (which can both run as co-witness btw) but this is supposed to be the fastest target acquisition technique for close targets (0-150M). Great background on co-witness sighting here.

Right now I’m leaning towards Troy Battlesights for the fixed option and undecided on the red dot. Candidates include the always cost-effective Leapers UTG compact red/green dot and the Bushnell TRS-25

Eventually I reckon I will end up with an SDN-6… More on that in a future article.

The stripped lower receiver will get some love:

  • Lower parts kit- gotta run an H2 buffer with the 9″ (a heavier buffer performs better in shorter gas systems)
  • 3lb Timney trigger
  • Lightweight yet solid stock- probably a Magpul CTR, potentially an ACE Skelton
  • A solid handgrip- Magpul or Mako Group are likely candidates

 If you’re not sure yet I’m excited to bring this all together. This is a whole different 

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