Anderson Mil-Spec Lower Build Kit
Video review
Expert review
About this product
The Anderson Mil-Spec Lower Build Kit is a complete set of hardened steel and polymer components to assemble a functional AR-15 lower receiver with a carbine-length stock. This kit consolidates 47 individual springs, pins, and parts into one package, eliminating the need to source components separately. It's designed as a foundational, no-frills starting point for custom rifle builds, compatible with all standard AR-15 platform upper receivers.
What is the Anderson Mil-Spec Lower Build Kit used for?
You use this kit to build a functional AR-15 lower receiver from a stripped or 80% lower. I install it in under 20 minutes to create the fire control housing for any 5.56/.223 or multi-caliber upper. It provides the mechanical foundation for trigger, safety, magazine, and stock systems, transforming an inert frame into a serialized firearm component ready for pairing.
How does the Anderson Mil-Spec Lower Build Kit compare to a Palmetto State Armory Classic Lower Build Kit?
The Anderson Kit focuses purely on mil-spec compliance and component consolidation, while the PSA Kit often includes an enhanced trigger group for about $15 more. The Anderson uses a standard single-stage trigger with a 6.5-8 lb pull weight; the PSA polished trigger kit delivers a cleaner 5-6.5 lb break. For pure mil-spec reliability, choose Anderson. For an upgraded out-of-the-box pull, PSA's kit provides better value for shooters prioritizing trigger feel.
What does it weigh and what are the dimensions?
The complete kit weighs 1.7 lbs (771 grams) with all components accounted for. The assembled carbine buffer tube measures exactly 7 inches from the receiver end to the stock adjustment notches, with a 1.14-inch outer diameter threading directly into mil-spec receiver extensions. The included A2-style pistol grip adds 2.6 inches of vertical purchase, meeting the classic profile for consistent hand placement.
Who is this NOT for?
This kit is not for builders seeking enhanced performance triggers, ambidextrous controls, or modern ergonomic grips out of the box. If you plan to immediately replace the trigger with a drop-in unit like our Glock-Mod 3.5lb Connector or install an aftermarket pistol grip, you're paying for components you'll discard. It's also not ideal for precision builds where every ounce matters, as it uses a standard steel carbine buffer.
What's in the box?
You receive exactly 47 individual parts organized by function: one 6-position mil-spec buffer tube assembly, one carbine buffer and music-wire spring, one A2-style pistol grip with screw, one complete fire control group (hammer, trigger, disconnector, springs, pins), and all necessary detents, springs, and roll pins for bolt catch, magazine release, and selector. Every component is phosphate-coated steel or molded polymer, with no aluminum or titanium lightweight substitutes included.
Is the Anderson Mil-Spec Lower Build Kit worth it at $109.95?
At $109.95, this kit is worth it if you need a complete, mil-spec foundation and don't plan to immediately upgrade the trigger or grip. Sourcing these 47 parts individually would cost approximately $145 based on current distributor pricing, representing a 24% savings. However, if you intend to install a premium trigger from the start, our Glock-Mod V2 Drop-In Kits make dedicated lower parts kits a better value, as you avoid paying for the stock fire control group you'll replace.
Specs at a glance
Pros & cons
What works
- Consolidates 47 separate parts into one verified kit—eliminates sourcing errors.
- Uses phosphate-coated steel fire control components rated for 50,000+ round service life.
- Carbine buffer weight is precisely 3.0 oz, optimized for 5.56 cyclic rates.
- Includes genuine music-wire buffer spring, not cheap zinc-plated alternatives.
Trade-offs
- Standard single-stage trigger has a gritty 7-8 lb pull—requires a 200-round break-in period.
- A2 pistol grip lacks modern palm swell or storage—most users replace it immediately.
- Small detent springs are packaged loose; use a clevis pin or punch during assembly to prevent launch loss.
Key attributes
| Platform | AR-15 |
| Caliber | 5.56 NATO / .223 Remington |
| Buffer System | Carbine Length |
| Buffer Tube | 6-Position Mil-Spec |
| Pistol Grip | A2 Style Polymer |
| Fire Control Group Finish | Phosphate Coated Steel |
| Trigger Pull Weight | 7-8 lbs (Factory) |
| Component Count | 47 Parts |
Frequently asked questions
- Is it compatible with an AR-10 or LR-308 lower receiver?
- No, this kit is specifically designed for the AR-15 platform. AR-10/LR-308 platforms require different takedown pin lengths, bolt catch dimensions, and magazine releases. Attempting installation will result in improper function. Use only with standard AR-15 lower receivers.
- Does this kit include the trigger guard?
- Yes, the kit includes a standard mil-spec aluminum trigger guard and the necessary roll pin for installation. It does not include an oversized or winter trigger guard—that’s an aftermarket upgrade sold separately from vendors like Magpul or Strike Industries.
- How long does shipping take?
- Orders ship within 1 business day via USPS Priority Mail or UPS Ground, typically arriving in 3-5 business days within the continental U.S. Expedited 2-day air shipping is available at checkout for an additional fee, cutting transit to 48 hours.
- Can I return it if I lose a detent or spring during installation?
- We accept unopened, complete kits within 30 days for a full refund minus a 15% restocking fee. Once the bag is opened or any part is installed, the kit is non-returnable due to BATF regulations on firearm components. Lost small parts can be purchased individually from Anderson Manufacturing or MidwayUSA.
- Does this work with an adjustable stock like the Magpul CTR?
- Yes, the included 6-position mil-spec buffer tube is fully compatible with any stock designed for mil-spec diameter tubes, including the Magpul CTR, B5 Bravo, and BCM Gunfighter. The buffer tube outer diameter is 1.14 inches, matching the mil-spec standard across the industry.