Big Dragon M120 upgrade spring for UK airsoft AEG

Big Dragon M120 AEG Spring

£3.95

M120 rated spring for a meaningful jump in muzzle velocity
Delivers roughly 120 m/s, around 380 to 400 FPS on 0.20g BBs
Fits standard Version 2 and Version 3 AEG gearboxes
Steel construction for consistent compression and long life
Great choice for DMR and semi-only field builds
Ideal for replacing tired stock springs or tuning a project gun

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Description
Specification

More power, more range

When your rifle needs more reach, the main spring is where it starts. The Big Dragon M120 AEG Spring lifts muzzle velocity to around 120 m/s, roughly 380 to 400 FPS on a 0.20g BB, making it a popular choice for DMR and semi-only field builds that need to reach out.

Consistent, durable steel

Made from steel for reliable compression shot after shot, it slots into standard Version 2 and Version 3 gearboxes, so it works across most M4, M16 and AK style platforms.

Know your limits

An M120 typically pushes past full auto site limits, so it is best suited to semi-only or DMR roles. Final FPS depends on your cylinder, barrel and air seal, and you should always chronograph before play and check your site’s rules.

Build it to last

A stronger spring loads the gearbox harder, so pair it with a high-torque motor, a solid piston and a good spring guide for reliability. Not confident inside a gearbox? Our Kent airsoft repair and Tech-It service can fit and chrono it. Browse more airsoft upgrade parts to complete the job.

Product information reviewed by James Smith. Every gun is checked & serviced by our Rochester workshop before dispatch.

General
Brand	Big Dragon
Other
Rating	M120
Approx muzzle energy	Around 1.44 joules on 0.20g BB
Approx velocity	Around 120 m/s (approx 380 to 400 FPS on 0.20g)
Compatibility	Standard V2 and V3 AEG gearboxes
Material	Steel
Part type	AEG main spring
Fitting level	Intermediate, gearbox disassembly required
Note	Final FPS varies with cylinder, barrel and air seal

Recommended upgrades & accessories

Frequently asked questions

What FPS will an M120 give me?

As a guide, an M120 spring produces around 120 m/s, roughly 380 to 400 FPS on a 0.20g BB. The exact figure depends on your cylinder, barrel length, piston and air seal.

Is an M120 site legal?

It depends on your site's limits. Around 380 to 400 FPS suits many DMR and semi-only categories but often exceeds full auto limits. Always check your site's FPS rules and chronograph before play.

Which gearboxes does it fit?

It is a standard-size AEG spring that fits common Version 2 and Version 3 gearboxes, covering most M4, M16 and AK style platforms.

Do I need other upgrades to run it?

For reliability at this power, a high-torque motor, a good air seal and a sturdy piston and spring guide are recommended, as the stronger spring puts more stress on the internals.

Can you fit and chrono it for me?

Yes. Our in-house Kent airsoft repair and Tech-It service can install the spring, check the internals and chronograph the rifle so you know your real FPS.

Big Dragon M120 AEG Spring