polarstar jack retroarms alignment kit v2 1 m4 ar15

Version 2.1 of the hop-up alignment system, designed for M4 / AR15 AEG HPA replicas using:

• PolarStar JACK engine (drop-in HPA kit, compatible with a wide range of V2 gearboxes with a centerline nozzle).
• RetroArms hop-up chamber for M4/AR15 (high-precision CNC chamber, designed for a solid, stable, and reliable fit in HPA builds).

This kit ensures precise alignment between the JACK nozzle and the RetroArms chamber, reducing play, improving feeding, and providing a more consistent base for HPA setups with V2 split / ICS gearboxes.

Compatibility

Component	Compatibility
HPA Engine	PolarStar JACK
Hop-up Chamber	RetroArms M4 / AR15
Base Replica	M4 / AR15 AEG
Gearbox	V2 / ICS SPLIT

What’s included in the kit

• Rear clip for mounting via rear pin or fixed stock
• Base with housing for M3 inserts (brass optional)
• Side clip for routing the JACK HPA line
• Top locking cap for the RetroArms chamber
• Rear plate with mounting point for an M5 screw (extra reinforcement)

Installation and setup

1. Printing and preparation

   • Print parts with 65–80% infill
   • Lightly sand internal/contact areas for a clean fit
   • If needed, apply dry lubricant or wax on sliding surfaces

2. Assembly on the replica

   • Insert the base into the lower and install the M3 inserts
   • Place the rear clip aligned with the rear pin or stock mounting point
   • Install the RetroArms chamber with the inner barrel; the top cap locks the assembly and keeps the barrel centered
   • Route the JACK HPA line through the side clip to prevent rubbing or kinks

3. Final fixing

   • Secure the rear plate with an M5 screw and washer for maximum rigidity
   • Check that the JACK nozzle enters the RetroArms chamber centered and that feeding is consistent
   • Perform dry tests and adjust hop-up according to BB weight and bucking

Required components (not included)

• 4× M3 × 4.2 mm inserts
• 4× M3 × 8 SHCS screws

Lower receiver recommendations

Using a metal ICS lower is recommended for maximum rigidity.
If you prefer to print your own lower, these Gearbox v2 Lower "Universal lower part" models are compatible:

• Version 3
• Version 4.2
• Version 4.3 MTW

You can find them HERE.

3D printing parameters

• Estimated print time: ~1 h 30 min
• Recommended material: PLA+
• Layer height: 0.10 mm – 0.15 mm

Manuals

Installation and setup manuals are available in the Manuals section on the website or on the project’s Discord server.