New Frontier Armory’s C-9 Billet Lower Receiver is the best way to start a custom 9mm AR build. You can save money and build your very own 9mm AR rifle exactly the way you want it configured and shoot for less! The C-9 uses Glock magazines and will accept any 9mm, .40 S&W or .357 SIG upper receiver.

If you have never shot a 9mm AR, you are missing out on low cost, low recoil, pistol steel shooting fun. The simple blow back system needs no gas tube, is reliable and easy to build. Short barrels? Short as you want them with no gas issues. Eight inch barrels sound crazy as an AR build, but they make great 9mm pistols and light enough to shoot all day with one hand.

The New Frontier Armory (NFA) C-9 lower was designed to fit and drop free Glock OEM small frame pistol magazines. It has also been thoroughly tested with Magpul GL17 9mm pistol magazines. Although it accepts and shoots other aftermarket magazines (Promag, KCI, Kahn, etc) some slight modification may be needed to get them to drop free from this lower because of the varying tolerances.

Specifications and Features of the C-9 Stripped AR-9 Lower Receiver:

  • Machined from 7075-T6 aircraft grade billet aluminum
  • Matte black hard-coat anodized per Mil 8625 Type 3 Class 2
  • Precision machined magazine well with beveled feed lip for easy mag swaps
  • Machined and engraved to be compatible with 45 and 60 degree short throw fire control selectors such as the BAD_ASS ST 45 Lever
  • Caliber marking of “Multi” so it can be used with different pistol caliber uppers
  • Compatible with most standard AR-15 components  and most aftermarket parts
  • Take down pin spring and detent hole is threaded for a 6-32 set screw for easy capturing (hardware included)
  • Upper tension screw behind grip screw (threaded hole with hardware included) to adjust any “slop” out of vertical fit between upper and lower
  • Ambidextrous trigger finger rests with grooves (above and below mag release / mag catch)
  • Threaded bolt catch pin (Threaded hole and hardware)
  • Integrated large opening “winter” trigger guard
  • Proprietary magazine catch assembly and ejector is included and installed at the factory
  • Manufactured to MILSPEC (where applicable) on state of the art CNC equipment for consistent quality parts and exacting tolerances

When you are picking parts for a build, you have to consider compatibility and tolerances. There is no MilSpec for the AR9, the Colt SMG is the reference. Some companies may have designs that don’t match each other, some companies may not maintain tolerances which allow compatibility. I have several 9mm ARs from different companies. I went with New Frontier Armory for all the parts on this build. I knew they would fit and be compatible with any other quality parts.

For a Glock magazine build, you will need an AR-9 Bolt Carrier Group that has relief cuts to clear the Glock style magazines.  I love the NFA BCG9, not only will it run with traditional Colt magazines and Glock magazines, but it will handle MP-5 magazines used in NFA’s C-5 9mm AR. One bolt for every magazine. Why would you buy anything else?

NFA sells a specific lower parts kit (LPK) with just the parts needed to build the C-9 lower receiver, buy any standard AR-15 LPK will work.  You will not need the magazine catch assembly, bolt catch roll pin, or trigger guard that are normally included with standard kits, so why buy them?

Although its not technically required, you should get a specific 9mm buffer, longer and heavier than the standard AR model. The 9mm bolt carrier group is shorter than a standard bolt carrier group.  You can use a carbine buffer with a spacer (Quarters are a perfect fit, add change until the bolt stops where you want it. If a spacer costs more than $1.25, you might want to reconsider). The reason for this is to limit the BCG travel to the rear so it doesn’t come back forward and smash the bolt catch hard enough to break it, this was a problem with the original Colt SMG.

New Frontier Armory 9mm AR Pistol Build: A Hand Full of Heaven
Colt SMG Model RO635 Photo courtesy of Colt

The New Frontier Armory 8oz Blowback Buffers are specifically designed for 9mm AR pistol caliber carbines. They are longer and heaver to meet the increased recoil impulse and shorter stroke of direct blow back ARs.

Conventional ARs use a direct impingement AR to cycle the weapon. This blows gas through a tube to cycle the bolt. The bolt is locked into place while firing. Pistol Caliber AR’s (9mm, .40, .357 Sig, .45, etc) use Blowback Operation.

With a Blowback system the bolt doesn’t lock. The only thing slowing down the action is the combined masses of the bolt and buffer along with the resistance of the spring. If there is not enough mass, there is more felt recoil that can break parts and crack receivers. With Blowback ARs there is no Gas Block to adjust so your only option for tuning is to adjust the buffer weight.

Made in America, the Extra Heavy 8-ounce Blowback Buffer from New Frontier Armory is the perfect tool for taming direct blowback.



New Frontier Armory 9mm AR Pistol Build: A Hand Full of Heaven
New Frontier Armory 8 oz pistol buffer

The blowback operation of the 9mm AR-15 drives a very heavy bolt (normally 16 ounces) much harder than a standard AR-15 BCG. The energy of the 9mm bolt needs to be

The Standard AR rifle buffer from the original full size ARweighs 5.2oz. The standard carbine buffer is about 3 oz, it has three internal steel weights.

Heavy carbine buffers (traditional design) replace steel weights with tungsten weights. Each time one is replaced, weight increases approximately .8oz.

H Buffer: 3.8oz

H2 Buffer: 4.7oz

H3 Buffer: 5.6oz

Colt SMG 2 piece mechanical Buffer:  5.47 ounces

NFA’s special blowback length buffers weigh 8 oz and 10 oz.
Colt SMG buffer on left, NFA 8 ounce 9mm buffer on the right.

The NFA buffer shoots softer and runs quieter than any conventional AR buffer. Its weight and length have been optimized for the 9mm application so it runs reliably, softens recoil and stops the bolt just behind the bolt catch using any 9mm ammo type. It dampens bolt impact for a soft landing which completely eliminates spring vibration and noise.

I went with the 9mm Priemum 8 inch barrel (1:10 twist) barrel and 7 inch MLOK free float hand guard from NFA. I like the way it looks and it is a great pistol size. It is accurate past 100 yards.

People spend big money on muzzle devices. I went with the basic M-16 flash hider in 9mm. There is not a lot of gas coming out of a 9mm, even with a short barrel, but I don’t like my hand close to a compensator. I have been burned before.

The lower looks great, everything works and it went together like pork and beans. The finishing touch was the SB-MINI Pistol Stabilizing Brace. The SB Tactical Mini is the lightest, minimalist interpretation their original SB15 that challenged the ATFE and started the AR pistol revolution. If weight and footprint are a consideration, the SB-MINI is the best solution.

I put Magpul back up sights and a SIG SAUER ROMEO (1×25 mm). The Romeo 3 red dot reflex sight is perfect for close and mid ranges where this gun operates. It is light, bright and just perfect for this build.

ETS magazines and loaders make carbines and pistols run great. They are east to use and let you see how many rounds you have left. There are shooters who mock magazine loaders. If you are shooting a lot of rounds, you know you need a loader. The ETS loader feeds right out of the box and is faster than any other pistol system I have seen.

All together, this pistol is magic. I only have 200 rounds through it but I am sold. The parts are quality, the design is advanced and refined. I look forward to making a lot of empty brass with this pistol for may years to come.

Photos by Mark Miller