ACM Metal M4 Hop Unit

£4.95

Durable metal build resists cracking under high rate of fire
Fits most M4 / M16 AEGs with a Version 2 gearbox
Holds hop settings more securely than tired stock chambers
Reliable BB feeding to cut jams and misfeeds
Ideal upgrade over a worn or broken plastic chamber
Beginner-friendly fit, trusted by experienced techs

In stock

Guaranteed Safe Checkout

Why Buy From Platoon Stores

In-House Repair Workshop in Rochester Kent

Kent's Only Authorised 5.11 Tactical Retailer

UKARA Registered Retailer

What our customers are saying

Be the first to leave a review.

Write a Review

There are no reviews yet.

Description
Specification

Swap flex for stability

The ACM Metal M4 Hop Unit (AC99166) replaces a soft or cracked plastic chamber with a tougher metal alloy build. Under high rate of fire, plastic chambers can flex and let the hop wander, whereas metal stays put, giving you more consistent BB feeding and a steadier hop from shot to shot.

Wide M4 platform fit

Designed for M4 and M16 pattern AEGs on the standard Version 2 gearbox, it slots into a huge range of popular electric rifles. It works with standard AEG hop rubbers and inner barrels, so your existing internals carry straight over.

Reliability where it matters

A worn chamber is a common cause of misfeeds and lost accuracy. Fitting a fresh metal unit tightens up feeding, reduces jams and restores dependable performance, making it a smart, low-cost upgrade or repair.

Fit it yourself or let us help

Installation involves opening the upper receiver and setting the hop once fitted. If you would prefer a professional touch, our Kent airsoft repair service can install it, and more spares are in our airsoft accessories range.

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

General
Brand	ACM
Other
Part Number	AC99166
Type	Hop-up chamber
Compatibility	M4 / M16 AEG
Gearbox	Version 2
Material	Metal alloy
Adjustment	Adjustable hop
Calibre	6mm BB
Use	Standard AEG hop rubber and inner barrel

Recommended upgrades & accessories

Frequently asked questions

How is a metal chamber better than plastic?

Metal resists flexing and cracking under sustained firing and high rate of fire, and it tends to hold hop adjustment more securely, giving more consistent BB flight over time.

Which rifles will it fit?

It suits M4 and M16 pattern AEGs on a standard Version 2 gearbox, one of the most common platforms in airsoft.

Does it include internals?

It is supplied as the chamber. It accepts standard AEG hop rubbers and inner barrels, so you can transfer your existing parts across.

Is it suitable for a first upgrade?

Yes. It is a popular first internal upgrade and a straightforward replacement for a worn stock chamber, though basic tech confidence helps with hop setup.

Do I need to be 18 or hold UKARA?

No. It is an internal spare part rather than a firearm, so there is no age restriction and no UKARA requirement.

ACM Metal M4 Hop Unit