Description
The CMMG MOD4SA is a semi-auto, forged 7075-T6 aluminum stripped lower receiver for building an AR-15 pattern rifle. It’s the serialized “firearm” component that houses the trigger, safety, and magazine, designed to accept standard AR-15 upper receivers in 5.56x45mm/.223 caliber. At its core price of $100.10, it’s a solid, no-frills foundation for a custom build. I’ve used several of these as the starting point for budget-friendly rifles and they’ve never let me down—they’re the definition of a workhorse part. This specific CMMG MOD4SA Semi-Auto AR-15 Forged M4 Stripped Lower Receiver 5.56x45mm /.223 Caliber 30 Round model is a classic choice for builders who want reliability without paying for a fancy rollmark.
Key Features
- Forged 7075-T6 Aluminum Construction: This is the same high-strength aerospace-grade alloy used in military-spec (mil-spec) receivers. It can handle serious round counts and hard use.
- Stripped Receiver Format: You get just the lower receiver itself. This lets you select your own trigger, grip, stock, and buffer kit to perfectly match your needs and budget.
- Full Mil-Spec Compatibility: The dimensions and pin locations are to military specifications. This means it will accept the vast majority of aftermarket AR-15 parts and uppers without issue.
- Semi-Auto Fire Control Pocket: The lower is machined for a standard semi-automatic trigger group, making it straightforward to build a compliant rifle.
- Anodized Finish: Provides a durable, corrosion-resistant surface that’s ready for final finishing or painting if desired.
Specifications & Details
| Specification | Detail |
|---|---|
| Material | Forged 7075-T6 Aluminum |
| Caliber | 5.56x45mm NATO / .223 Remington |
| Magazine Compatibility | Standard AR-15 / STANAG pattern (30-round common) |
| Fire Control | Semi-Auto |
| Finish | Matte Black Anodized |
| Compatibility | Mil-Spec AR-15 Upper Receivers & Parts |
Look, the beauty of a stripped lower like this is its potential. It weighs in at just under a pound before you add any parts, giving you a blank canvas. You can pair it with a simple PSA upper for a truck gun or match it with a high-end BCM or Aero Precision upper for a duty-ready rifle. The point is, it’s versatile. And here’s the key for first-time builders: because it’s mil-spec compatible, assembly is straightforward. With basic tools and patience, you can complete it—no gunsmithing required for the lower parts kit installation. This unit ships to Missouri and compliant US states, making it an accessible starting point for builders across the country.
Who This Lower Receiver Is For
This CMMG lower is ideal for the first-time AR builder who wants a trusted, affordable foundation. It’s also perfect for the seasoned shooter assembling a dedicated .22 LR upper host or a simple beater rifle where you don’t want to tie up an expensive receiver. If your goal is a basic, functional rifle without paying for branding or unnecessary features, this is your part. It’s not for someone seeking an ambidextrous control set or a fully finished rifle out of the box—that’s not its job.
Pros & Cons
Pros: The price is a major advantage at just over a hundred bucks. The forged 7075-T6 construction is proven and tough as nails. Full mil-spec compatibility means endless parts options and easy assembly. CMMG has a strong reputation for quality, so you’re not buying from an unknown manufacturer.
Cons: As a stripped receiver, it requires additional investment in parts and tools to become functional. The finish, while durable, is a basic matte anodizing that some might find utilitarian. It lacks modern convenience features like an integrated trigger guard or flared magazine well, but that’s typical for this price point.
Frequently Asked Questions
Q: Is this a complete firearm?
A: No. This is a “stripped” lower receiver. It is the serialized part legally considered the firearm, but it requires the installation of numerous other components (lower parts kit, buffer tube assembly, stock, grip) and the mating of a complete upper receiver to function.
Q: What parts do I need to buy to complete this?
A: At a minimum, you’ll need a Lower Parts Kit (LPK), a buffer tube kit (buffer tube, spring, buffer, end plate, castle nut), a pistol grip, and a stock. You will also need a complete upper receiver assembly and a magazine. Remember, an FFL transfer is required for firearm purchases, including this receiver.
Q: Will this work with any AR-15 upper?
A: It is designed to be compatible with any mil-spec AR-15 upper receiver. I’ve personally mated these with uppers from Palmetto State Armory and Anderson Manufacturing without any fitment issues. Always check for fit with any upper, but mil-spec standards make mismatches rare.
If you’re ready to start your build with a dependable, straightforward foundation, this CMMG lower is available at firearms-missouri.com for Missouri residents and nationwide.
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