Retro Arms CNC Hop-Up Chamber Pro, M4/AR15

The Retro Arms CNC Hop-Up Chamber Pro is a complete hop-up chamber for AR-15/M4 AEGs, CNC-machined from EN AW 7075 aircraft aluminium and anodised. The Pro version builds on Retro Arms' well-known Basic chamber but has an adjustable feed lip, so the chamber can be adapted to receivers and magazines that don't seat or feed correctly.

The hop-up chamber is one of the parts that affects accuracy the most: it centres the barrel, holds the bucking and determines how the BB is fed in. Many AEGs have problems with magazines that don't lock or don't feed cleanly, because the feed lip sits at the wrong height relative to the receiver. The Pro chamber solves this by letting you adjust the height in 0.2 mm steps with the included shims.

What makes the Pro version different

Key features of the Retro Arms Hop-Up Chamber Pro:

• Adjustable feed lip: The feed lip height is adjusted in 0.2 mm steps with the included shims. Without shims it sits as on the Basic chamber, so you can adjust from a known starting position.
• Barrel collet nut: Instead of a centring ring, a collet nut at the front clamps barrel and chamber together and eliminates barrel movement. It fits barrels with an outer diameter of typically 8.4–8.5 mm.
• R-hop ready: The chamber is prepared for R-hop, so you can upgrade the hop system later without changing the chamber.
• O-ring in the feed lip: An O-ring in the feed lip holds the last BBs in place when you change magazines, so they don't fall out.
• 7075 aluminium: CNC-machined from EN AW 7075 aircraft aluminium and anodised – stiffer and more dimensionally stable than plastic and standard chambers. The fine-tuned main body and feed lip suit most hop-up buckings.

Maintenance and safety

• Secure the adjustable feed lip with medium-strength threadlocker after setting it, as Retro Arms recommends.
• Make sure the barrel doesn't rotate in the chamber when the collet nut is tightened.
• Set the feed height gradually and test with your own magazines before locking the setting.
• Our workshop in Aulum, Denmark can fit and adjust the chamber to your receiver and magazines.