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 preloaded spring nozzle and electronic pressure/volume adjustment).
- Bullgear 2024 chamber (new CNC hop-up version with dual adjustment system and geometry optimized for HPA).
This kit ensures precise alignment between the F2 nozzle and the Bullgear 2024 chamber, eliminating lateral play and maintaining consistent nozzle-to-chamber contact for maximum feeding consistency in demanding HPA builds.
Compatibility
| Component | Compatibility |
|---|---|
| HPA Engine | PolarStar F2 M4 / V2 |
| Hop-up Chamber | Bullgear 2024 |
| 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 HPA tube/line.
- Front locking top cap designed specifically for Bullgear 2024.
- 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 on sliding areas 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 Bullgear 2024 chamber with the inner barrel; the top cap locks the assembly in place.
- 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 F2 nozzle enters the Bullgear 2024 chamber perfectly centered without lateral play.
- Configure the F2 pressure (recommended 45–120 PSI) and perform dry feeding tests.
Required components (not included)
- 4× M3 × 4.2 mm threaded inserts
- 4× M3 × 8 SHCS screws
Lower receiver recommendations
For maximum rigidity it is recommended to use the ICS metal lower receiver.
If you prefer to print the lower part, the following 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
- 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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