CYMA CM.621 M4 KeyMod Airsoft Rifle

  • MOSFET Inside
  • Microswitch Trigger
  • Quick Change Spring

Featuring a Microswitch Trigger, MOSFET and Quick Change Spring system with a tough Nylon Fibre exterior and included Battery & Charger, the CYMA CM.621 is possibly one of the greatest out-of-the-box guns on the market for the money.

Full description


The CYMA CM.621 M4 KeyMod AEG is an M4 based design which offers a lightweight and tough KeyMod Rail System with 20mm RIS adaptors included for your choice of attachment type. It has a world of features out of the box which would be unheard of in most competing models in the same price range, and offers excellent value for money. With a MOSFET, Quick Change Spring, included Battery & Charger and reinforced Polymer externals, this AEG is the perfect starter gun.

The front of the AEG has a 14mm CCW Thread underneath the Bird Cage Flash Hider which will allow you to install Supressors, Tracer Units, Muzzle Brakes and more. Simply unscrew the grub screw from the Flash Hider and twist to remove. The Handguard is a KeyMod Rail System which comes included with side and lower 20mm adaptors, to give you flexibility in the type of attachments you can use. The Top 20mm Rail runs the full length of the Handguard and down to the back of the Receiver, which is ready for Sights and Scopes to attach, and is also where you will find a set of Flip Up Ironsights which can be removed if you don't want them. At the rear of the Receiver you will notice an Ambidextrous Sling Plate, which means that you can attach a Sling from either side of the Gun, depending on whether you're Left or Right Handed. The stock is a Sliding Crane Stock design and houses your Battery, connected to a Mini Tamiya Connector. To access the Stock, simply squeeze the tabs on the Butt Plate and pull it away as well as the blanking plate underneath. We recommend either a 9.6v 1600mAH NiMH Crane Battery or 7.4v <2000mAH Crane LiPO Battery for the best fit.

Deep inside the CYMA CM.621 there is a MOSFET to protect the Electrical Components of the AEG, as well as a Microswitch Trigger which is very pleasant to use. The benefit of a Microswitch Trigger is much faster response from the gun, as well as removing the chance of burnt-out Trigger Contacts from a traditional design. The gun has a Quick Change Spring system which lets you change the Main Spring in seconds, once the Gearbox has been removed from the Receiver. This is an amazing feature for Airsofters who play at lots of different sites with varying Power Limit rules, and need to quickly change the FPS of their gun. Please note that technical skills are still required to remove the Gearbox from the gun. The gun has an Adjustable HOP Unit which will apply backspin to your BBs, and potentially increase effective range when combined with a Heavyweight BB (0.25g+) and the correct settings on the Adjustment Wheel. To make changes to the HOP, pull back the charging handle and look inside the dust cover to access the Adjustment Wheel.

Included in the box is an 8.4v 1100mAH NiMH Crane Battery and UK Plug Charger, which will make the gun fire but will be inferior in quality to an aftermarket set. Also included is an Alloy 300rnd High Cap magazine which is filled from the top via the fill window and wound from the bottom with the clockwork wheel to feed BBs. If you're looking for the ideal starter gun to get you on your way to Airsoft skirmishing, and/or are looking for fantastic value out of the box, then the CYMA CM.621 is just that.


  • Microswitch Trigger
  • MOSFET Installed
  • Quick Change Spring
  • Tough Nylon Fibre Polymer
  • Battery & Charger Included
  • Full Metal Gearbox
  • Alloy Outer Barrel Assembly
  • Alloy Buffer Tube
  • Rear Wired / Mini Tamiya
  • 14mm CCW Thread
  • 300rnd High Cap Magazine
  • Flip-Up Ironsights
  • Perfect Starter Gun
  • Excellent Value for Money
  • Sliding Crane Stock
  • Fast Trigger Response
  • KeyMod Railed Handguard
  • 20mm Receiver Rail
  • Ambidextrous Sling Plate
  • Adjustable HOP
  • Gear Style HOP Adjust

Package Includes

  • CYMA CM.621 M4 KeyMod Airsoft Rifle
  • 300rnd High Capacity Magazine
  • 8.4v 1100mAH NiMH Crane Battery
  • UK Plug Charger
  • User Manual



Weapon Construction External
Weapon Type
Assault Rifle
Over 18 Only Icon
Over 18
Icon UKARA - United Kingdom Airsoft Retailer Association
Defence / UKARA Required
Yes, No,
FPS Icon
FPS (Feet Per Second), using 0.20g BB
Approx. 315fps ± 10%, using 0.20g BB
Site Legal Icon
Site Legal, using 0.20g BB
Included Items
  • Magazine
  • Instruction Manual
  • Battery
  • Charger
Skill Level Icon
User Skill Level
Patrol Base - Warning Icon
Free Gift Battery Warning

Weight and Dimension

Weight KG Icon
Weight (KG)
Approx. 2kg
Weapon Length Collapsed
Length (Collapsed)
Weapon Length Extended
Length (Extended)


Colour Wheel Greyscale
Primary Colour
Two Tone Icon
Pre Two-Toned
Construction Icon
Alloy outer barrel assembly, magazine, buffer tube and trim. Polymer handguard, receiver, pistol grip and stock.
Weapon Construction External
External Construction
Gearbox Icon
Internal Construction

Weapon Specific

Power Source Icon
Powered By
Blowback Icon
Weapon Platform
AR Platform, M4 / AR15 / M16,
Magazine Style Icon
Magazine Style
STANAG, AR Platform,
Fire Select Icon
Fire Selector
PatrolBase | Fire Select Safe
Patrol Base | Fire Select - Semi Automatic
Semi Automatic
Patrol Base | Full Automatic
Full Automatic
Weapon Safety Features Icon
Safety Features
Trigger Lock
Shooter Configuration Icon
Shooter Configuration
Right Handed
Weapon Configuration Icon
Weapon Configuration
Weapon Scale Icon
Weapon Scale
Suggested BB Weight


Hop-Up Unit Icon
Hop-Up Unit
Hop-Up Unit Adjuster Icon
Hop-Up Adjuster
Hop-Up Unit Location Icon
Hop-Up Location
Behind mock bolt when charging handle pulled to the rear


Weapon Furniture Icon
  • Railed Handguard
  • Flip-Up Ironsights
  • Railed Receiver
  • Sliding Stock
  • Threaded Outer Barrel
  • Ambidextrous Sling Plate
Rail System Icon
Rail System
20mm RIS / RAS , KeyMod ,
Icon Stock Positions
Stock Setting
Weapon Length Extended
Stock Positions
6 Position
Sight Type Icon
Sight Type
Iron Sights
Sling Plate Icon
Sling Options
Buffer Plate


Icon Thread Type
Outer Barrel Thread Type
Icon Thread Direction
Outer Barrel Thread Direction
CCW (Counter Clockwise)
Outer Barrel Thread Size

Magazine Specific

Magazine Type
High Capacity, AEG,
Magazine BB Capacity
Approx. 300 Rounds
Magazine BB Fill Method
Fill Window
Magazine BB Fill Location

Electric Gun Specific Information

Gearbox Icon
Gearbox Version
V2 Gearbox
Wiring Icon
Gearbox Wiring
Rear Wired
Spring Change Icon
Gearbox Quick Change Spring
Digital Trigger Icon
Gearbox Electronic Trigger
Battery Specific
Battery Connector
Patrol Base | Icon | Mini Tamiya
Mini Tamiya
Included Battery
Battery Configuration
Battery Type
Battery Voltage
Battery Amperage
Suggested Battery
Suggested Battery Type
Suggested Battery Configuration
Suggested Battery Voltage

Product Testing Data

Notepad Icon
Test Description
Notepad Icon
Tested Using
ASG Blaster 0.20g BBs
Notepad Icon
Test Date

Detailed Power Tests

FPS, using 0.20g BB
Approx. 315fps, using 0.20g BB

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