PolarStar F1 + Silent Industries ALPHA alignment kit for M4 AEG (v2.1)

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

• PolarStar F1™ HPA Conversion Kit (universal drop-in for V2 gearboxes, programmable pneumatic system with dual-stage firing and high efficiency).
• Silent Industries ALPHA M4/16 AEG/HPA Chamber (CNC hop-up chamber with TRUE-TDC, tension ring system, and full bucking lip support, designed as a “game changer” for HPA builds).

This version of ALPHA is from before 2026; the body is rounded.

This kit ensures solid and precise alignment between the F1 nozzle and the ALPHA chamber, reducing typical HPA issues such as double feeding, mid-cap syndrome, and BB position inconsistency.
The result is more stable feeding and improved shot consistency, fully taking advantage of the direct airflow and fast response of the F1.

Compatibility

Component	Compatibility
HPA Engine	PolarStar F1 M4 HPA Conversion Kit
Hop-up Chamber	Silent Industries ALPHA M4/16 AEG/HPA
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 (brass optional).
• Side clip for routing the HPA tube/line.
• Top cap for front locking of the ALPHA chamber, designed to respect the CNC body and barrel adjustment.
• 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 smooth fit.
   • Apply dry lubricant or wax if you want to make assembly and future maintenance easier.

2. Installation in the replica

   • Insert the base into the lower and install the M3 inserts.
   • Place the rear clip aligned with the rear pin or the stock mounting point.
   • Install the ALPHA chamber with its inner barrel; the top cap fixes the position and helps keep the barrel centered using the chamber’s own alignment groove.
   • Route the F1 HPA line through the side clip to avoid bends or unnecessary friction.

3. Final fixing and testing

   • Secure the rear plate with an M5 screw and washer to provide maximum rigidity to the assembly.
   • Verify that the PolarStar F1 nozzle enters the ALPHA chamber centered and that feeding is clean during dry tests and test firing.

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Required components (not included)

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

(Recommended purchase links are available in the generic hardware section of the store.)

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Recommended lower

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

• Version 3
• Version 4.2
• Version 4.3 MTW

You can find them HERE.

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3D printing parameters

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

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Manuals

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

Related products and articles

Similar product designs:

• PolarStar F2 + Silent Industries ALPHA alignment kit for M4 AEG (v2.1)
• PolarStar JACK + Silent Industries ALPHA alignment kit for M4 AEG (v2.1)
• Gate Pulsar-H + Silent Industries ALPHA alignment kit for M4 AEG (v2.1)

Technical articles for this topic:

• MAXX Model Hop-Up: Differences Between Models, Versions, and Compatibility with HPA Kits
• Silent Industries Alpha Hop-Up: Differences Between Versions and Compatible Kits