polarstar f2 retroarms alignment kit v2 1 m4 aeg hpa

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

• PolarStar F2 engine (dual-solenoid HPA engine with high pneumatic efficiency and programmable configuration).
• RETROARMS chamber (precision hop-up chamber with excellent bucking support and fine adjustment optimized for HPA).

This kit ensures perfect centering between the F2 nozzle and the RETROARMS chamber, eliminating lateral alignment issues that can cause feeding inconsistencies or double feeding. Fully compatible with ICS split systems and standard V2 gearboxes.

Compatibility

Component	Compatibility
HPA Engine	PolarStar F2 M4
Hop-up Chamber	RETROARMS
Base Replica	M4 AEG
Gearbox	V2 / ICS SPLIT

What the kit includes

• Rear clip for mounting via rear pin or fixed stock.
• Base with housing for M3 inserts (optional brass for maximum durability).
• Side clip for routing the F2 HPA tube/line.
• Front locking top cap specifically designed for the RETROARMS chamber.
• Rear plate with mounting point for an M5 screw (additional reinforcement).

Installation and adjustment

1. Printing and preparation

   • Print the parts with 65–80% infill.
   • Lightly sand internal areas and contact surfaces for a perfect fit.
   • Apply dry lubricant or wax on sliding surfaces to make maintenance easier.

2. Installation in the replica

   • Insert the base into the lower and install the M3 inserts in their housings.
   • Install the rear clip aligned with the rear pin or the stock anchor point.
   • Install the RETROARMS chamber with the inner barrel; the top cap locks the assembly while keeping the barrel perfectly centered.
   • Route the PolarStar F2 HPA line through the side clip to prevent rubbing or sharp bends.

3. Final fixation

   • Secure the rear plate using an M5 screw and washer for maximum rigidity.
   • Verify that the F2 nozzle enters centered into the RETROARMS chamber without lateral play.
   • Perform dry feeding tests and adjust the F2 pressure (recommended range: 45–145 PSI).

Required components (not included)

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

Lower receiver recommendations

It is recommended to use the ICS metal lower receiver for maximum rigidity in demanding builds.
If you prefer to print the lower part, the following Gearbox V2 Lower “Universal Lower Part” models are fully compatible:

• Version 3
• Version 4.2
• Version 4.3 MTW

You can find them HERE.

3D printing parameters

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

Manuals

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