Description
PolarStar JACK Direct Attachment Conversion Set
The PolarStar JACK Direct Attachment Conversion Set replaces the original front cylinder of a PolarStar JACK HPA engine and connects the engine directly to the Polarstar "Hop Up Thing" Chamber for AEG/HPA M4 V2. This creates a single rigid assembly consisting of the HPA engine, hop-up chamber and inner barrel.
In a conventional HPA installation, the gearbox shell positions the engine in relation to the hop-up chamber. Dimensional differences, movement between components or an incorrectly aligned gearbox shell can allow the nozzle to tilt or move sideways. Even a small alignment error can affect BB feeding, air seal, hop-up consistency and grouping.
The Direct Attachment system transfers the alignment function from the gearbox shell directly to the connection between the JACK engine and the hop-up chamber. The upper section of the gearbox shell is therefore no longer responsible for keeping the engine and hop-up correctly aligned.
Rigid monolithic assembly
The conversion set consists of two main components:
- PolarStar JACK Direct Attach Front Cylinder
- Internal threaded adapter
The original front cylinder is removed from the JACK engine and replaced with the Direct Attachment components. The compatible PolarStar hop-up chamber is then threaded directly onto the adapter.
Once assembled, the JACK engine, hop-up chamber and inner barrel form one rigid unit. Because the main components cannot move independently, the nozzle remains mechanically aligned with the inner-barrel bore.
Minimal nozzle deflection
According to PolarStar, the Direct Attachment system supports the nozzle with approximately 0.0025 inches, or about 0.064 mm, of clearance on each side. This tight support effectively prevents the nozzle from leaning or moving sideways while loading a BB.
Reducing nozzle movement can help prevent feeding and consistency problems commonly known as mid-cap syndrome. This can occur when pressure from a fully loaded mid-cap magazine affects the position of the hop-up chamber or nozzle.
Consistent BB loading and hop-up performance
When the nozzle loads each BB into the hop-up chamber in the same position and at the same depth, the contact between the BB, hop-up bucking and nub remains more repeatable.
Consistent BB positioning and nozzle engagement can support a more stable air seal, repeatable hop-up effect and tighter groupings. The system also removes the need to align the JACK engine by shimming it against the upper section of the gearbox shell.
Designed for advanced HPA builds
The JACK Direct Attachment Conversion Set is not a drop-in component for an unmodified gearbox. Because the engine connects directly to the hop-up chamber, the upper section of a conventional gearbox shell is no longer required and may need to be removed.
The electronics, trigger, selector and other lower gearbox components still require a suitable supporting structure. Depending on the build, this can be:
- A modified V2 gearbox shell
- A compatible replacement gearbox lower
- A suitable 3D-printed lower structure
- A completely custom chassis or replica body
The system can be used to correct alignment problems in an M4-style JACK build or as the foundation for a custom or 3D-printed HPA replica.
Compatibility
- Designed specifically for the PolarStar JACK HPA engine
- Replaces the original JACK front cylinder
- Compatible only with the Polarstar "Hop Up Thing" Chamber for AEG/HPA M4 V2
- Not compatible with conventional AEG or other aftermarket hop-up chambers
- Intended for modified V2 gearbox installations and custom builds
- Not a drop-in component for an unmodified gearbox shell
- This JACK version is not compatible with PolarStar F2 or Kythera engines
Required additional components
- PolarStar JACK HPA engine
- Polarstar "Hop Up Thing" Chamber for AEG/HPA M4 V2
- Compatible inner barrel
- Compatible hop-up bucking and nub
- Modified gearbox shell, compatible gearbox lower or custom supporting structure
- Compatible electronics, trigger and selector components
- Other air-system components required for operating the JACK engine
Installation notes
- The original front cylinder must be removed from the JACK engine.
- The original threaded gearbox interface must be removed from the compatible PolarStar hop-up chamber.
- Apply suitable grease to the internal sealing surface of the JACK adapter according to PolarStar’s instructions.
- The hop-up chamber is threaded directly onto the Direct Attachment adapter.
- Start the threads carefully to prevent cross-threading.
- Do not force the components together if the threads do not engage smoothly.
- The hop-up feed tube must be correctly aligned for smooth magazine insertion.
- The installation requires technical experience and modification of the gearbox or supporting chassis.
Installation guide
Read the official PolarStar Direct Attachment guide before beginning the installation:
PolarStar Direct Attachment Installation Guide (PDF)
Features
- Connects the PolarStar JACK directly to the compatible hop-up chamber
- Creates a rigid engine, hop-up and inner-barrel assembly
- Maintains precise nozzle-to-barrel alignment
- Effectively eliminates independent nozzle deflection
- Approximately 0.0025" / 0.064 mm nozzle clearance per side
- Helps reduce mid-cap syndrome
- Supports consistent BB loading and nozzle engagement depth
- Can improve air-seal and hop-up consistency
- Removes the need for gearbox-shell alignment shimming
- Suitable for modified V2 and custom HPA builds
Package contents
- PolarStar JACK Direct Attach Front Cylinder
- Internal threaded adapter
Not included
- PolarStar JACK HPA engine
- Polarstar "Hop Up Thing" Chamber for AEG/HPA M4 V2
- Inner barrel
- Hop-up bucking and nub
- Gearbox shell or replacement gearbox lower
- Electronics, trigger or selector components
- Air hose, regulator or HPA tank
- Replica or other components shown in product images
Technical specifications
- Manufacturer: PolarStar
- Product: JACK Direct Attachment Conversion Set
- Product type: direct-attachment conversion set for an HPA engine
- Compatible engine: PolarStar JACK
- Compatible hop-up chamber: Polarstar "Hop Up Thing" Chamber for AEG/HPA M4 V2 only
- Replaces: original PolarStar JACK front cylinder
- Construction: two-piece front-cylinder and adapter system
- Approximate nozzle clearance: 0.0025" / 0.064 mm per side
- Installation type: modified or custom installation
