Atlas Custom Works Gas Blowback Hop-Up Chamber for M4 GBB Rifle, Black

A GBB's hop-up chamber takes more abuse than any other internal part. Every shot sends a BB through it at high pressure, and the nozzle slams against it hundreds of times a minute. Plastic wears, deforms, and loses alignment. That's where a metal chamber like the ACW GB105 comes in.

What changes with metal. The GB105 is machined from solid metal at 40 mm length and 0.7 oz weight. Metal resists the repeated gas pressure cycles and nozzle impact that wear out polymer chambers. It holds its shape, which means the air seal stays consistent and your hop-up setting stays where you put it. That shot-to-shot consistency is what you actually feel when you're aiming.

Fit and compatibility. This is built for M4 GBB platforms. It replaces the factory chamber directly—no adapters, no modification. The black finish matches standard internal components. You'll need your existing inner barrel and hop-up assembly; this is the housing, not a complete hop-up system.

Before you buy. This is a replacement part for M4 gas blowback rifles only. It does not work with AEGs, pistols, or other platforms. If your current chamber is worn, cracked, or causing inconsistent hop-up, this is the upgrade. If you're building from scratch, you'll also need a compatible inner barrel, bucking, and nub.