Aero Precision M4E1 / A.T.L.A.S. Caliber Ready Enhanced Builder's Chassis System - CRBCS-15M

$ 962.99

Sold Out

Aero Precision


The Aero Precision M4E1 / A.T.L.A.S. Caliber Ready Enhanced Builder's Chassis System the perfect base for your next high-end AR build. Meticulously engineered and machined from high strength aerospace grade aluminum forgings, the M4E1 Chassis System is the lightest weight system on the market today, retaining the strength and rigidity of forged aluminum while giving you a sleek, ergonomic and aesthetically pleasing custom billet look. Each M4E1 chassis is hand finished and matched in-house for the utmost in operational and cosmetic perfection that our customers have come to expect from us at Ground Zero Precision and from Aero Precision. 

Caliber Ready makes it easy for you to build a rifle in any AR-15 caliber you choose! All you have to add is the following and you're all set:

  • The barrel, gas system & muzzle device for the caliber rifle you want to build
  • The caliber specific bolt carrier group
  • The caliber specific buffer system

Aero Precision M4E1 Enhanced Lower Receiver - Complete

Aero Precision M4E1 Lower Receiver

Aero's M4E1 Enhanced Complete Lower Receiver is the perfect base for your custom AR-15 build. This complete lower features the new M4E1 lower receiver and has been upgraded by Ground Zero Precision with some of the most popular upgrade parts on the market today including a CMC Triggers™ curved 3.5lb drop-in trigger, Strike Industries enhanced AR grip, Armaspec ambidextrous 45 degree safety selector, stainless anti-rotation pins and TCB extended magazine release, Hogue overmolded 6-position carbine stock, center QD endplate and more!


  • M4E1 Stripped Lower Receiver - Anodized Black
  • CMC Triggers 3.5lb single stage drop-in trigger - Curved
  • Magpul MOE K2 Pistol Grip - Black
  • Hogue™ Overmolded 6 position adjustable carbine stock - Black
  • Enhanced lower parts kit
  • 6 position carbine receiver extension - Mil-Spec
  • These parts are installed

Aero Precision M4E1 Gen II Threaded Upper Receiver

Aero Precision M4E1 Threaded Upper

The M4E1 threaded upper receiver features a new angular machined design that helps it stand apart from standard mil-spec upper receivers. This upper receiver features the same enhanced body profile as our M4E1 Enhanced Upper Receiver but is threaded to accept a standard AR15 barrel nut. It is forged from 7075-T6 Aluminum, precision machined to work with all mil-spec AR15 parts and includes the port door and forward assist pre-installed.

The M4E1 threaded upper receiver is designed to pair perfectly with Aero's new M4E1 lower receiver, giving you a billet looking receiver set at a fraction of the billet price.


  • New enhanced forging that gives the upper receiver a "billet look"
  • New picatinny profile that blends seamlessly with our Enhanced and ATLAS Series Handguards
  • M4 Feedramps
  • .250 takedown pin holes
  • Lazer engraved T-marks
  • Includes port door and forward assist


  • M4E1 Threaded upper receiver - Anodized black
  • Port Door and Forward Assist installed
  • These parts are installed

15" Aero Precision A.T.L.A.S S-ONE Handguard - M-Lok

Aero Precision ATLAS S-ONE Handguard

The new Aero Taper Lock Attachment System (ATLAS) is both functional and aesthetically pleasing. It features 2 mirrored tapered locking nuts that provide evenly distributed clamping pressure across a custom engineered barrel nut with use of a turnbuckle screw. A ratcheting detent further secures the design while providing positive registration during installation. By design, the even pressure of the ATLAS system avoids distortion of the handguard often seen with current applications during installation.

Weighing in at a mere 7.95 ounces, the A.T.L.A.S (Aero Taper Lock Attachment System) S-ONE slim line contoured free-floating handguard is the lightest weight 15" full featured handguard on the market today. Designed to fit seamlessly with Aero's new M4E1 upper receiver and featuring a unique design profile allowing for quick hand placement in the fore hand grip area for quick target acquisition, repeatability and shooter comfort. 

  • Precision machined from aerospace grade 7075-T6 aluminum
  • 1.30" Inside diameter
  • 1.50” Outside diameter
  • Contoured fore hand grip area for grip repeatability and shooter comfort
  • Front and rear picatinny top rails
  • Eliminated center of top rail for weight reduction
  • Indexing grooves in 12:00 position for positive grip control
  • Quick disconnect sling socket at the 3, 6 and 9 o’clock positions
  • Compatible with low profile gas blocks
  • Compatible with all M-Lok attachments and accessories
  • 1 Piece free float design
  • Patented A.T.L.A.S. (Aero Taper Lock Attachment System) barrel nut and mounting hardware included
  • Solid single piece anti-rotation mounting system
  • Type III Class 2 Hard Coat Anodized Finish
  • Compatible with mil-spec AR-15 upper receivers and barrels



FFL Instructions, Terms and Conditions (PLEASE READ!!!):
- Any items placed on the same order as a lower receiver will also be shipped to the FFL. If you would like additional items shipped to you directly, please place them on a separate order.
- Please enter your information or the receiving party's (the person that will be picking it up) information AS WELL AS the name, email and a good contact phone number for the FFL dealer you want us to ship your receiver to in the SPECIAL INSTRUCTIONS box while checking out. We will obtain the shipping address and other necessary information directly from them.
- If the dealer you are using to transfer a firearm has not sent us a currently updated FFL to put on file or is uncooperative with our request there will be an extended period of time needed to process your order.

There will be a 30% restocking fee on all lower receivers returned because of failed background checks. 

Federal law requires that you be 21 years or age or older to purchase a stripped receiver or frame. If a frame or receiver can only be made into a long gun (rifle or shotgun), it is still a frame or receiver not a handgun or long gun. However, they still are "firearms" by definition, and subject to the same GCA limitations as any other firearms. See Section 921(a)(3)(b). 18 U.S.C. Section 922(b)(1) makes it unlawful for a licensee to sell any firearm other than a shotgun or rifle to any person under the age of 21.