The modern shooter looking for a reliable, serviceable AR-15 platform at a realistic price needs an honest assessment of options built for duty use and range days alike. This review focuses on the core features that make a rifle durable, accurate, and easy to maintain for defensive and general-purpose roles.

SIG SAUER RM400 The SIG SAUER RM400 is an affordable, high-quality AR-15 chambered in 5.56x45mm NATO and built around a direct impingement gas system with a rotating locking bolt. It features a corrosion-resistant Nitride-treated barrel and an aircraft-grade aluminum forged lower receiver, combining longevity and proven construction at a competitive price point. Shop this product

Key features and why they matter

The RM400’s Nitride-treated barrel resists corrosion and wear better than untreated steel, which translates to consistent performance in harsh environments and reduced maintenance. The direct impingement gas system is familiar to most AR users—lightweight and simple—while the rotating locking bolt provides reliable lockup for 5.56 NATO pressures.

Ergonomics and modularity

With a full-length Picatinny rail and a full handguard, the rifle supports optics, offset sights, lights, and other accessories without sacrificing a clean mounting surface. The 6-position collapsible stock gives adjustable length of pull for different body armor or shooting positions. Compatibility with M16-type magazines ensures broad ammo-magazine interoperability and easy resupply.

Applications for 5.56 NATO

Chambered in 5.56x45mm NATO, the RM400 is suited for home defense, law enforcement, and general training. The caliber offers manageable recoil, good terminal performance with appropriate ammunition, and widespread availability. For shooters focused on duty-style setups, the RM400 balances capability and affordability—listed at $1000.99 and categorized under Semi Auto on the shop page.

The forged aircraft-grade aluminum lower contributes to a durable platform that tolerates everyday use while keeping weight reasonable. Whether building a patrol rifle or a well-rounded range gun, the RM400’s feature set is pragmatic and field-oriented. View product details and pricing

For buyers comparing duty-ready ARs, the SIG SAUER RM400 offers essential features—Nitride-treated barrel, forged lower, full Picatinny rail, collapsible stock, and M16 magazine compatibility—at an accessible price. Check current availability and complete your purchase on our shop page where the retailer handles checkout. Check availability

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