SA M4 Keymod (SA-F02 FLEX™ Gen.2) - Black / Tan

M4 Assault Rifle

The M4 is a compact automatic rifle developed in the United States based on the popular M16 assault rifle. It was designed to meet the need for a lighter and shorter version of the M16, suitable for use in close quarters and urban combat. In the 1960s, the M16—developed by Armalite and adopted by the U.S. Army—became the base design for the M4. In the 1980s, the first M4 prototypes appeared, featuring a shorter barrel and a telescopic stock to improve maneuverability in confined spaces.
In the 1990s, the M4 was officially adopted by the U.S. armed forces as the standard-issue carbine, replacing older models like the M3 and M9. The rifle is capable of both semi-automatic and full-auto fire, making it a versatile weapon. Thanks to its low weight, compactness, and reliability, the M4 quickly became popular among soldiers. It saw extensive use in conflicts such as the Iraq and Afghanistan wars and became an iconic weapon of modern U.S. military forces.
In addition to the standard model, many M4 variants exist, equipped with various accessories and upgrades to meet the specific needs of military units.
The airsoft AEG assault rifle M4 in the base FLEX™ series by Specna Arms focuses on lightweight nylon body without sacrificing excellent finish and fit. The fiberglass-reinforced body is more durable than common low-grade metal alloys, making it ideal not only for beginners but also for advanced players who prefer fast-paced gameplay like speedsoft, where every gram counts. This type of body is used in models like the CZ Scorpion Evo or MP7.
The FLEX series is essentially the sibling of the CORE line, where the latter features CNC metal handguards, while the FLEX line comes with nylon handguards. The internal Gen2 parts are top-tier, as this model now includes a reinforced QSC gearbox AETHER™ V2 (same as in the high-end PRIME series) and a MAGNUS™ hop-up chamber with TDC pressure system. The trigger unit is powered by the Gate X-ASR MOSFET.

FLEX™ Gen.2 Internal Components

The M4 Keymod (SA-F02 FLEX™ Gen.2) replica is equipped with the GATE MOSFET X-ASR module from Poland. It ensures safe trigger control, protects internal components, improves trigger response, extends battery life, and increases the rifle’s rate of fire. It also enables safe use of Li-Po batteries 7.4V and 11.1V. Thanks to its built-in diagnostic LEDs, the module can even detect basic issues in the rifle. The gun also features a fully upgraded gearbox called ÆTHER, rated for springs up to M140. Accuracy is ensured by a 6.03 mm inner barrel, paired with a Helium Flat-Hop bucking inside the reworked MAGNUS™ chamber with TDC pressure system.
Also included is the QSC ESA quick spring change system, allowing you to swap springs for stronger or weaker ones depending on your needs. The spring can be changed without removing the gearbox from the body—you simply access it through the buffer tube.

M4 Keymod (SA-F02 FLEX™ Gen.2) External Build

The Specna Arms M4 Keymod (SA-F02 FLEX™ Gen.2) replica stands out with its high-quality nylon body, which has a matte finish and looks very realistic. Thanks to fiberglass reinforcement, it’s very durable and lightweight. The outer barrel is made of metal, and the screws, dust cover, and pins are even made of steel. The ergonomic AR15 design and modern construction offer comfortable handling and easy control—this rifle simply feels great! The Keymod handguard allows for mounting various accessories like grips, AN/PEQ boxes, or flashlights. With its adjustable Crane-style stock, this replica is ready for any scenario and supports various battery types (Buffer Stick, Nunchuck, or Crane). All in all, it’s a rifle that combines low weight and high-performance internals with an attractive price.

Plastic body parts:

• Body
• Buffer tube
• Handguard
• Pistol grip, stock, and sights as seen in the Edge series

Metal parts:

• Outer barrel with 14-mm thread for suppressor
• Flash hider
• Charging handle for hop-up adjustment
• Various screws, pins, and small parts made from steel

Technical Specifications

• Power type: AEG
• Material: Nylon, polymer, metal
• Length: 795–880 mm
• Weight: 2350 g
• Power: 120 m/s (1.48 J)
• Inner barrel length: 363 mm
• Inner barrel diameter: 6.03 mm
• Hop-up: Adjustable, TDC
• Fire mode: Semi, Full Auto
• Barrel thread: 14-mm CCW
• Handguard: KeyMod
• Recommended battery: 11.1V Li-Po (not included)
• Connector: T-Dean
• Battery type: Crane (Buffer stick, Nunchuk)
• Magazine capacity: 300 BBs (Hi-Cap)
• Motor type: Carbon

Package Contents

• Specna Arms M4 AEG rifle
• 300 BB Hi-Cap S-MAG magazine
• Flip-up sights
• Spare M90 spring for CQB
• Specna Arms stickers
• User manual

Warning

• Some brands produce overpowered springs (e.g. M130 may perform like M140–150) that may exceed the gearbox’s rated durability. Use only Specna Arms springs. For other brands, it’s recommended to use M120 springs to avoid potential damage from mislabeled products.
• When installing a spring with progressive winding, make sure the tighter end faces the spring guide and points outward from the gearbox.
• Never store the rifle with the battery connected.