Version 2.1 of the hop-up alignment system, designed specifically for M4 AEG HPA replicas using:
- PolarStar F2 engine (dual-solenoid HPA engine with precise control of pressure and air volume).
- Begadi Neptune PRO chamber (high-precision hop-up chamber optimized for HPA with fine bucking adjustment).
This kit ensures perfect alignment between the F2 nozzle and the Neptune PRO chamber, eliminating lateral misalignment issues and improving feeding consistency in high-rate-of-fire builds. It is fully compatible with ICS split gearbox systems.
Compatibility
| Component | Compatibility |
|---|---|
| HPA Engine | PolarStar F2 M4 / V2 |
| Hop-up Chamber | Begadi Neptune PRO |
| 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).
- Side clip for routing the PolarStar F2 HPA line.
- Front locking top cap designed specifically for Neptune PRO.
- 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 to achieve a smooth and clean fit.
- Apply dry lubricant or wax on sliding surfaces if desired.
2. Installation in the replica
- Insert the base into the lower and install the M3 inserts.
- Mount the rear clip aligned with the rear pin or stock mounting point.
- Install the Begadi Neptune PRO chamber with its inner barrel; the top cap locks the assembly while keeping the barrel perfectly centered.
- Route the F2 HPA line through the side clip to prevent bends.
3. Final fixation
- Secure the rear plate using an M5 screw with washer for maximum rigidity.
- Verify that the PolarStar F2 nozzle enters the Neptune PRO chamber perfectly centered without lateral play.
- Perform feeding tests and adjust the Neptune PRO hop-up according to your BB weight and bucking.
Required components (not included)
- 4× M3 × 4.2 mm threaded inserts
- 4× M3 × 8 SHCS screws
Lower receiver recommendations
For maximum rigidity in demanding builds, it is recommended to use the ICS metal lower receiver.
If you prefer to print your own lower part, the following Gearbox V2 Lower “Universal Lower Part” models are 100% 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.
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