Sig Sauer M400 / 516 Stripped Lower Receiver, 5 Pack

# Sig Sauer M400 / 516 Stripped Lower Receiver, 5 Pack

## Build with Confidence – OEM-Grade Foundations

Every serious AR-15 build starts with a stripped lower receiver that balances precision machining with rugged reliability. This 5-pack of Sig Sauer M400/516-compatible lowers gives builders and shops a cost-effective foundation for multiple projects without compromising on material integrity. Machined from 7075-T6 aluminum and hardcoat anodized, these receivers meet the same dimensional standards as factory Sig Sauer components. Ideal for bulk builds, backup inventory, or custom shop work.

### Key Specifications
– **Material:** 7075-T6 aluminum (aircraft-grade)
– **Finish:** Type III hardcoat anodized (matte black)
– **Compatibility:** Sig Sauer M400, 516, and most mil-spec AR-15 parts kits
– **Fire Control Group Pocket:** Auto-sear ready (M16 cut)
– **Threaded Bolt Catch Pin:** Secures without drift punches
– **Markings:** Clean, unbranded design for custom engraving
– **Includes:** 5x stripped lower receivers (no small parts included)

## Feature Breakdown

**Precision Machining for Tight Tolerances**
CNC-milled from forged 7075-T6 aluminum, these lowers maintain consistent wall thickness around critical stress points like the buffer tube threads and takedown pin holes. The threaded bolt catch pin simplifies assembly compared to traditional roll-pin designs, reducing marring during installation. Tighter-than-average magwell dimensions ensure minimal wobble with PMAGs and USGI magazines.

**Anodizing That Stands Up to Hard Use**
The Type III hardcoat finish exceeds standard anodizing for abrasion resistance, particularly where the safety selector and trigger pins rotate under repeated use. Unlike cheaper finishes that wear to bare aluminum around high-friction areas, this retains corrosion protection even after thousands of cycles. Matte black provides a neutral base for Cerakote or other custom coatings.

**Compatibility Without Compromise**
While optimized for Sig Sauer’s M400/516 platforms, these lowers accept most mil-spec upper receivers, triggers, and buffer systems. The auto-sear cut allows compatibility with aftermarket fire control groups while remaining 922(r) compliant when paired with US-made components. Note that some aftermarket billet uppers may require minor fitting due to non-standardized tolerances.

**Bulk Value for Builders**
Purchasing in a 5-pack reduces per-unit cost for gunsmiths, training facilities, or enthusiasts planning multiple builds. Unbranded design avoids conflicts with personal or shop logos when custom engraving. Each receiver is individually bagged to prevent shipping damage, with serial number areas left blank for FFL processing.

## Compatibility Notes
– **Upper Receivers:** Fits most mil-spec AR-15 uppers (check rear takedown pin fitment)
– **Triggers:** Accepts all drop-in and mil-spec FCGs (including forced-reset designs)
– **Buffer Systems:** Works with carbine, rifle, or PDW tubes (requires endplate installation)
– **Pistol Builds:** Compatible with arm braces and pistol buffer kits (consult local laws)

## Installation Overview
1. **Parts Required:** Lower parts kit, buffer tube assembly, stock/grip, and FCG.
2. **Tools Needed:** Armorer’s wrench, roll pin punches (1/16″ and 3/32″), and vise blocks.
3. **Process:** Install trigger guard first, then pivot/takedown pins, followed by bolt catch and mag release.
4. **Final Check:** Ensure safety selector moves freely before attaching upper receiver.

## FAQ

**Q: Are these lowers serialized?**
A: No – they ship blank for your FFL to serialize per ATF requirements before transfer.

**Q: Will a Geissele SSA-E trigger fit?**
A: Yes, all mil-spec trigger pockets accommodate aftermarket FCGs, including high-end models.

**Q: Do they include jigs for 80% completion?**
A: No – these are 100% stripped lowers ready for immediate parts installation.

**Q: Can I use an ambidextrous safety selector?**
A: Yes, the receiver is cut for standard and ambi selectors without modification.

**Q: Are these compatible with .308 builds?**
A: No – designed exclusively for AR-15/.223/5.56 platforms.

## Warranty + Shipping
– **Warranty:** Lifetime guarantee against manufacturing defects (excludes user modifications).
– **Shipping:** Discreet packaging with tracking. FFL required for delivery – provide dealer info at checkout.
– **Note:** Some states restrict lower receiver shipments; verify local laws before ordering.

*No frills, no markup – just OEM-quality receivers for your next build.*nn