C-5 Billet Lower

New Frontier Armory

(8 reviews) Write a Review
0.95 LBS
C-5 Lower
Pistol Cal
Black Ano or RAW (Media Blast Only)
Magazine Type:
7075 Billet Aluminum

Stripped C-5 Billet Lower (MP5 Mag) – Packaged w/ Hardware

Other Specifications and Features of the Stripped C-5 Billet Lower (MP5 Mag):

  • 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
  • Compatible with moststandard AR-9 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, feed ramp, 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
  • Save money by building your own AR-9 rifle from the ground up exactly the way you want it configured and shoot for less!
  • **NOTE — You must use an upper that has widening cuts to accept the larger width MP5 Magazines — We sell three versions of C-5 Uppers that can be found HERE.

Pistol caliber specific LPK is available by CLICKING HERE

Magazines can be found HERE **NOTE: ETS magazines may require slight sanding to ensure proper fitment due to variations from factory H&K Magazines. We have yet to find any fitment issues with HK, Zenith, or KCI mags.


QUESTION: What type of magazines will fit in this lower?

ANSWER: The lower was designed to fit and drop free factory MP5 9mm magazines. It has also been thoroughly tested with many aftermarket magazines to fit and drop free. Although it accepts and shoots other aftermarket magazines (KCI, etc) some slight modification may be needed to get them to drop free from this lower because of the varying width measurement we have seen when checking these magazines to H&K MP5 factory specifications.

QUESTION: Do you offer a reliable last round / empty magazine bolt hold open (LRBHO) System for this lower?

ANSWER: NO, like the original MP5 platform, there is no LRBHO function. You must use either our C-5 Slick Side Upper or our C-5 Non Reciprocating Side Charging upper as they are widened to accept the MP5 magazines. Other manufacturers make uppers cut for MP5 mags as well, but we can't guarantee their compatibility at this time.

QUESTION: What bolt carrier group will work with a MP5 magazine fed AR-9?

ANSWER: The AR-9 BCG that we sell (CLICK HERE for AR-9 BCG) will work in our MP5 Mag AR-9

QUESTION: What LPK will work with this lower?

ANSWER: Although we sell a specific LPK with just the parts needed to build the C-5 lower receiver HERE, 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 LPKs.

QUESTION: Do I need to use a special buffer when I build my AR-9?

ANSWER: Although its not technically required, it is advised that you either use a 9mm buffer (longer and heavier than carbine) or a spacer in your buffer tube before you place your spring in. 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. The 9mm BCG is shorter than a standard BCG. You can use a carbine buffer with a spacer (WHICH YOU CAN PURCHASE BY CLICKING HERE).

The New Frontier Armory C-5 Stripped Billet AR-9 lower receiver is proudly MADE IN THE USA by hard-working American men and women.


This is a serialized item considered to be a firearm by BATFE. This item must be shipped to a Federal Firearm License (FFL) holder. All BATFE, GCA & NFA rules apply! This item must be shipped to a Federal Firearm License (FFL) holder. You will be prompted at checkout to pick an FFL to ship to in your area using our FFL Locate tool.YOU will be responsible for checking with your local FFL to ensure this weapon is legal in the state that you reside and that they will accept this weapon on your behalf and transfer it to you.New Frontier Armory, LLC will NOT be responsible for any shipping or admin charges incurred by packages not being accepted by the FFL you choose during checkout.

Weight: 0.95 LBS
Dimensions: 9.50 x 4.50 x 2.25 in

8 Reviews Hide Reviews Show Reviews

  • 5
    Love this lower!

    Posted by Joel on 1st Mar 2024

    Built an AR-9 with this C-5 Lower, C-5 Upper, Faxon barrel, and Maxim Defense bolt. Only shot 100 rds so far, but it functioned flawlessly. Very smooth feeding and extraction. Great to be able to use the MP-5 mags I already have. Love it!

  • 5
    Solid, reliable, and a good value

    Posted by Paulie on 26th Dec 2023

    This lower receiver is well made, worked reliably without any modifications or tuning, and is well priced in the market. I installed a PCC specific cassette type fire control unit, finished the rest of the lower parts installation, put it on a BRN-9 upper, and went to the range. Ran Turkish MKE 30rd mags; worked perfectly. A mix of 9mm, some steel cased Tula, Winchester NATO 124, S&B 115 ball, etc. Highly recommended.

  • 5
    Solid, Reliable, excellent Value

    Posted by Paulie on 21st Dec 2023

    I paired this lower with a BRN-9 Upper. Fit was trouble free, function is perfect. I am using Turkish MKE made 30rd magazines. Fit is just right, not too loose, not too tight, and drop free. I find these MKE mags are a good value for factory MP5 magazines, being built to the same standard as the HK marked magazines, but almost half the price. This receiver required no modification to run perfectly with the BRN-9 upper. Fit and finish is excellent, and the installed proprietary parts are of good quality. Highly recommended.

  • 5

    Posted by Antonio fasio on 20th Dec 2023

    Just like the two other New frontier receivers I have, this thing is just solid. Looks sharp and I’m pretty sure I could hit it with a hammer and need a new hammer lol . And mp5 mags just makes it so damn cool

  • 5
    Lower rec

    Posted by Derik Oakes on 2nd Nov 2023

    It looks great and is built very well , no scratches and functions perfectly

  • 5
    Review C5 receiver

    Posted by Ray on 14th Oct 2023

    Upon receiving the lower I was impressed by the craftsmanship put into this receiver. It was purchased as a “future” build. I’ve always liked the MP5 and as a result, purchased a bunch of mags in the past. I’ve since let the weapon go but still had magazines. I was looking for a AR platform that would accept the MP5 mags and the C5 fit the bill.

  • 5

    Posted by Dustin on 4th Aug 2023

    The fit and finish is great I’m planning on running it on the brn9 and still waiting on it to come in and will do a review on both

  • 5
    Mp5 mag lower, c5 lower

    Posted by Kimberly on 6th Mar 2023

    One of the best AR lower I ever bought. Can't wait to get it finished. Highly recommend to get one if you don't already. What's better then a mp5 mag lower? Not much. Pure awesomeness

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