PolarStar JACK Direct Attachment + PolarStar HopUp · Alignment Kit V2.1 · SR25 DMR AEG HPA

Version 2.1 of the alignment system for the SR25 DMR AEG HPA platform with a V2.5 gearbox.

This kit is designed to mount a PolarStar JACK engine using the Direct Attachment system and a PolarStar HopUp chamber. The Direct Attachment connects the engine, hop-up chamber, and inner barrel into a single rigid assembly, reducing movement between components and keeping the nozzle centered relative to the chamber.

The result is a cleaner, more stable installation for SR25 DMR builds, providing more consistent feeding and reducing the need for manual alignment adjustments.

Compatibility

Component	Compatibility
HPA Engine	PolarStar JACK
Connection System	PolarStar Direct Attachment for JACK
Hop-up Chamber	PolarStar HopUp
Base Replica	SR25 / AR10 DMR AEG
Gearbox	V2.5
Configuration	HPA

Important: This kit requires a PolarStar JACK compatible with Direct Attachment, the corresponding Direct Attach front cylinder, and a compatible PolarStar HopUp chamber.

What's Included in the Kit

• Mounting base specifically designed for the SR25 DMR platform.
• Rear support for attachment using the rear pin or stock mounting system.
• Side guide for the HPA line.
• Chamber support to stabilize the assembly inside the upper receiver.
• Rear plate with a mounting point for an M5 screw.
• Geometry designed for the PolarStar JACK + Direct Attachment + PolarStar HopUp assembly.

Advantages of Direct Attachment

• Connects the engine, hop-up, and inner barrel into a single rigid assembly.
• Keeps the nozzle aligned with the hop-up chamber.
• Reduces play between the gearbox, engine, and chamber.
• Eliminates the need for push springs to keep the chamber in position.
• Provides more consistent feeding in DMR configurations.
• Simplifies alignment adjustments during installation.

Installation and Adjustment

1. Preparing the Kit

   • Print the parts with 65–80% infill.
   • Lightly sand the internal and contact surfaces until a clean fit is achieved.
   • If necessary, apply dry lubricant or wax to sliding surfaces.

2. Installing the Direct Attachment

   • Install the Direct Attachment front cylinder on the PolarStar JACK.
   • Fit the internal adapter according to the system configuration.
   • Thread the PolarStar HopUp chamber onto the adapter until it forms a solid assembly with the engine.
   • Check that the top of the chamber is correctly oriented before final tightening.

3. Installing the Assembly in the Replica

   • Insert the engine + Direct Attachment + hop-up assembly into the SR25 upper receiver.
   • Install the kit's mounting base and rear support.
   • Route the HPA line through the side clip, avoiding tight bends, pinching, or friction.
   • Secure the rear plate with an M5 screw and washer to reinforce the assembly.

4. Final Checks

   • Verify that the magazine can be inserted and removed without forcing the hop-up chamber.
   • Perform dry feeding tests.
   • Adjust the hop-up according to BB weight and the configured power output.
   • Check that the assembly has no lateral or longitudinal movement inside the upper receiver.

Recommendations

• Use an inner barrel and bucking suitable for a DMR configuration.
• Avoid using a spring between the chamber and barrel when the Direct Attachment already keeps the assembly rigid.
• If magazine insertion is too tight, check the chamber's positioning before modifying other components.
• Check the Direct Attachment adapter's tightness during routine maintenance.
• Configure the PolarStar JACK in accordance with your field's power limits and regulations.

3D Printing Settings

• Recommended Material: PLA+
• Layer Height: 0.10 mm–0.15 mm
• Recommended Infill: 65–80%
• Supports: Only when required by the chosen print orientation
• Recommended Finishing: Fine sanding of adjustment and contact surfaces

Manuals

Installation and adjustment manuals are available in the Manuals section of the website or on the project's Discord server.