First Look: New AR-15 Uppers From SIG Sauer

Change up your AR with these ready-to-roll upper receivers.

by
posted on September 21, 2025
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SIG Sauer AR-15 Upper receiver

SIG Sauer is coming out with two new complete, drop-in AR-15 upper-receiver assemblies. These complete kits include everything you need to upgrade your AR lower.

MCX-SPEAR LT 9-inch Upper AR Conversion Kit 300BLK - FDE

The MCX-SPEAR LT developed for the Special Forces community and allows you to convert any AR15 lower into either an SBR with a stock and the appropriate paperwork or a large-format pistol with a brace.  

Features:

  • Adapts with any M4/AR15-spec lower assembly
  • Dual-rod recoil assembly eliminates buffer system
  • M4 adapter allows for picatinny rail folding stock capabilities
  • Adjustable gas system for suppressor optimization
  • Quick-change barrel design allows to easily swap calibers and barrel lengths
  • Gas-piston design reduces exposure to carbon fouling
  • Designed to go 20,000 rounds before any maintenance-part replacements
  • Ambidextrous charging handle with gas deflector
  • Replaceable parts (cam path follower, feed ramp, forward assist/deflector, charging handle locking pins) allow for longer receiver life over standard AR designs.
  • Tapered bolt design functions more reliably and lasts longer than standard square-lug M4 bolt designs.
  • Nitride coated, cold hammer forged barrel for more accuracy and barrel life

SIG AR Upgrade Kit

Upgrade your AR rifle or lower assembly with a complete, drop-in M400 upper assembly. This kit includes all the necessary components for a complete swap, including a two-stage match trigger as well as the popular Tango-MSR LPVO 1-6X24mm second focal plane (SFP) riflescope. The free-floating handguard uses a new steel lockup design that significantly reduces handguard deflection by providing maximum rigidity and allows for accessories to be attached on all four sides with no effect on accuracy. The 2-Stage Matchlite Duo trigger provides a crisp 4.5-6.5-pound pull weight with a flat blade design for a precision feel.

Included Items:

Complete 16-inch 5.56 NATO upper assembly
SIG 2-Stage Matchlite Duo trigger
Tango-MSR LPVO 1-6X24MM (SFP)

16-inch 5.56 NATO M400 Upper Assembly Features:

  • Black Anodized Finish
  • Three-prong flash-hider accepts SLH & SLX suppressor systems.
  • Dual-clamp handguard locking system for reduced deflection
  • Low-profile gas block with mid-length gas system
  • High-quality, premium barrel

Tango-MSR LVPO 1-6X24mm Features:

  • High-performance 6X optical system with low-dispersion glass
  • Integrated thread-in throw leaver for quick magnification changes
  • Illuminated MSR BDC-6 reticle with 11 brightness levels
  • Lay-flat, flip-back lens covers included
  • Dependable waterproof, shockproof, and fog-proof performance
  • Includes Alpha-MSR one-piece aluminum cantilever mount

MSRP for the MCX-SPEAR LT 9-inch Upper AR Conversion Kit is $1,699.99, and the MSRP for the SIG AR Upgrade Kit is $1,199.99. More information on these items and other products from SIG Sauer is available at sigsauer.com.

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