Sig Sauer M400 / 516 Stripped Lower Receiver, 5 Pack

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Sig Sauer M400 / 516 Stripped Lower Receiver, 5 Pack

Build multiple rifles with this bulk pack of stripped lower receivers—machined to Sig Sauer’s specifications for compatibility with M400 and 516 uppers. These unfinished lowers ship raw, ready for your custom engraving, anodizing, or cerakote work. Ideal for builders stocking up on serialized components or assembling rifles for different calibers. Nationwide shipping available; no FFL required for receivers sold separately (check local laws).

Key Specifications

• Material: 7075-T6 aluminum forgings
• Finish: Uncoated raw aluminum (ready for customization)
• Compatibility: Sig Sauer M400, 516, and most mil-spec AR-15 uppers
• Fire Control Group: Accepts standard AR-15 triggers (not included)
• Pack Quantity: 5 stripped lowers
• Weight: 8.2 oz per receiver (without parts)

Feature Breakdown

These lowers are forged from 7075-T6 aluminum, the same material used in military-spec receivers, for consistent durability under heavy use. The raw finish allows for custom cerakote patterns or Type III hardcoat anodizing without stripping existing coatings. Tighter-than-average tolerances on the pivot and takedown pin holes ensure minimal play when paired with Sig uppers.

Each receiver includes threaded bolt catch and trigger guard holes but requires installation of all internal components (trigger, hammer, safety selector, etc.). The magwell is machined to accept both Gen 2 and Gen 3 PMAGs without modification. Rear shelf is pre-milled for optional storage compartments or QD sling mounts.

Builders will appreciate the clean, unbranded exterior—no logos or roll marks interfere with custom engraving for personal builds or resale. The fire control pocket is cut for both semi-auto and full-auto trigger groups (compliance with local laws is the buyer’s responsibility).

Note that these are not complete firearms; they require assembly with a parts kit, buffer tube, and upper receiver to function. The 5-pack bulk pricing is aimed at gunsmiths, small shops, or builders planning multiple projects.

Compatibility Notes

• Upper Receivers: Fits Sig Sauer M400, 516, and most mil-spec AR-15 uppers
• Triggers: Works with any AR-15 FCG (drop-in or mil-spec)
• Buffer Kits: Compatible with carbine or rifle-length systems
• Pistol Builds: Can be configured as pistol lowers (check ATF guidelines)

Installation Overview

Assembling these stripped lowers requires basic gunsmithing tools: a punch set, armorer’s wrench, and vise block. Install the trigger guard first, followed by the bolt catch and magazine release. The fire control group pins may need light fitting depending on your trigger choice. Final torque specs for the buffer tube should follow AR-15 industry standards (typically 35-40 ft-lbs).

FAQ

Q: Are these receivers serialized?
A: Yes, each lower has a unique serial number engraved per ATF requirements.

Q: Can I build a pistol with these?
A: Yes, if configured properly per ATF rules—never assemble into a rifle first if intending pistol use.

Q: Do they include jigs for engraving?
A: No, the raw finish is ready for professional laser engraving or roll marking.

Q: Will aftermarket grips fit?
A: Yes, the grip screw hole is standard AR-15 pattern.

Q: How do I finish the raw aluminum?
A: Most builders cerakote or anodize; raw aluminum can corrode if left unprotected.

Warranty & Shipping

Lifetime warranty against manufacturing defects. Shipping times vary by state due to local regulations. Receivers ship in protective foam within plain boxes—no external firearm markings. Must be 21+ to purchase in most states.

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