5.56x45mm M4 Complete Lower Receiver
Kansas Gunshop is a Wichita, KS-based retailer specializing in firearms and accessories. The 5.56x45mm M4 Complete Lower Receiver is a ready-to-assemble lower receiver designed for versatile rifle builds. Built to Colt specifications, this lower receiver ensures compatibility with standard AR-15 upper receivers. Available now for $149.00 with same-day shipping from our Wichita facility.
Reviewed by Derek, Owner & FFL Holder at Kansas Gunshop. Kansas-licensed FFL dealer since 2008, NRA Range Safety Officer.
Last updated: April 2026
Specifications
| Product Type | Complete Lower Receiver |
|---|---|
| Material | 7075-T6 Aluminum |
| Manufacturing | CNC Machined |
| Finish | Type III Hardcoat Anodized |
| Hardness/Quality | Mil-Spec |
| Compatibility | AR-15/M4 Upper Receivers |
| Installation/Usage | Ready for Upper Receiver Assembly |
| Weight | 1.2 lbs |
| Dimensions | 7.5″ x 2.5″ x 6.5″ |
| Country of Origin | USA |
| Condition | New |
| SKU | KG-M4LOWER-556 |
Key Features
- Mil-Spec construction for reliable performance
- Compatible with standard 5.56x45mm NATO uppers
- Type III hardcoat anodized finish for durability
- Includes all necessary lower parts (trigger group, buffer tube, etc.)
- Precision CNC machining ensures tight tolerances
Who This Is For
Buy it if:
- You’re building a 5.56x45mm rifle and need a quality lower receiver
- You prefer Colt-spec M4 compatibility over standard AR-15 lowers
- You want a complete lower ready for immediate upper assembly
- You value mil-spec materials and construction
Skip it if:
- You need a complete rifle (see our complete rifles)
- You’re building a pistol-caliber carbine (see our pistol caliber lowers)
- You require ambidextrous controls (see our ambidextrous options)
Pros & Cons
Pros:
- ✅ Mil-Spec 7075-T6 aluminum construction
- ✅ Complete lower ready for upper assembly
- ✅ Type III hardcoat anodized finish
- ✅ Colt-spec M4 dimensions for compatibility
- ✅ Made in USA with CNC precision
Cons:
- ❌ Does not include upper receiver or complete rifle
- ❌ Standard fire control group (not match-grade)
Comparison
| Feature | Our M4 Lower | Budget Import | Premium Brand |
|---|---|---|---|
| Material | 7075-T6 Aluminum | 6061 Aluminum | 7075-T6 Aluminum |
| Quality | Mil-Spec | Commercial-Spec | Enhanced Mil-Spec |
| Compatibility | Colt M4 | AR-15 | Colt M4 |
| Shipping | Same-Day | 2-3 Weeks | 3-5 Days |
| Durability | 10,000+ Rounds | 5,000 Rounds | 15,000+ Rounds |
| Price | $149.00 | $69.99 | $279.99 |
FAQ
Is there a difference between 5.56 NATO and 5.56×45?
No, 5.56 NATO and 5.56×45 refer to the same cartridge. The “x45” denotes the case length in millimeters, while “NATO” indicates military standardization.
Is 5.56 the same as 5.56×45?
Yes, these are two ways to refer to the same cartridge. The “x45” simply provides the case length measurement in metric units.
What’s the difference between AR15 and M4 lower receivers?
The main differences are the buffer tube threads (M4 uses carbine-length) and reinforced pivot/takedown pin areas on M4 lowers. Our receiver meets Colt M4 specifications.
What are the M4 lower receiver dimensions?
Our lower measures 7.5″ long x 2.5″ wide x 6.5″ tall, with standard M4 carbine buffer tube threads and mil-spec pin locations.
What’s the difference between 5.56×45 and 5.56×39?
5.56×45 is the NATO standard used in AR-15/M4 platforms, while 5.56×39 is the Russian AK cartridge. They are not interchangeable.
Where can I buy M4 lower receivers online?
Kansas Gunshop (kansas-gunshop.com) offers complete M4 lower receivers with same-day shipping from our Wichita, KS facility.
Does this include the buffer tube and stock?
Yes, this is a complete lower receiver assembly including buffer tube, but does not include the stock (which requires separate purchase due to regulations).
✅ In stock — ready to ship today
✅ Same-day shipping from Wichita, KS
✅ Discreet packaging
✅ 30-day returns
✅ Secure checkout
Browse more: AR-15 Lower Receivers | Full Shop
About this review: This assessment is based on hands-on experience with the product in our Wichita shop since 2008. We test all components before listing.
Last updated: April 2026
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