polarstar jack prowin alignment kit v2 5 sr25 dmr hpa

Version 2.5 of the hop-up alignment system, specifically designed for SR25 DMR HPA replicas (Designated Marksman Rifle) using a V2.5 long gearbox.
It combines the PolarStar JACK engine (compact high-power HPA engine, ideal for DMR configurations with extended nozzle travel) and the PROWIN chamber (precision hop-up chamber designed for sniper-style rifle builds).

This kit ensures perfect nozzle alignment in the V2.5 long gearbox, compatible with ICS lowers, eliminating lateral deviations that affect long-range precision in DMR builds. The V2.5 design is adapted for the longer nozzle travel and the specific geometry of the SR25 gearbox.

Compatibility

Component	Compatibility
HPA Engine	PolarStar JACK
Hop-up Chamber	PROWIN
Base Replica	SR25 DMR
Gearbox	V2.5 long (SR25)
Lower	ICS or universal

What the kit includes

• Reinforced rear clip for mounting via rear pin or fixed SR25 stock.
• Extended base with housing for M3 inserts (brass recommended for DMR builds).
• Dual side clip for stable routing of the HPA line in long rifle configurations.
• Front locking top cap adapted for PROWIN chambers and DMR barrels (6.01–6.03 mm).
• Rear plate with hole for an M5 screw (critical fixation for DMR precision).

Installation and adjustment

1. Printing and preparation

   • Print with 75–90% infill (extra rigidity for DMR builds).
   • Sand internal areas for precise fit, especially around the longer nozzle travel path.
   • Apply dry lubricant on all moving surfaces.

2. Installation in the SR25 replica

   • Insert the base into the ICS or universal V2.5 lower and install the M3 inserts.
   • Secure the rear clip using the SR25 long gearbox rear pin.
   • Install the PROWIN chamber and the DMR inner barrel; the top cap aligns and locks the assembly considering the longer JACK nozzle travel.
   • Route the HPA line through the dual side clips for stability in long rifle configurations.

3. DMR fixation and calibration

   • Secure the rear plate using an M5 screw + washer (critical for maintaining zero in DMR builds).
   • Configure the PolarStar JACK in semi-only mode (recommended 0.75–1.5 J for DMR).
   • Verify alignment using a borescope and adjust the PROWIN hop-up for 0.36–0.43 g BBs.

Required components (not included)

• 6× M3 × 4.2 mm inserts (extra reinforcement for DMR builds)
• 6× M3 × 10 SHCS screws (longer for V2.5 gearbox)
• 1× M5 × 12 screw + washer (rear plate fixation)

Lower receiver recommendations

Compatible with the original ICS lower receiver (recommended for DMR builds due to rigidity).
Printable universal alternatives for V2.5 gearboxes include:

• Gearbox V2 Lower “Universal Lower Part” Version 3
• Gearbox V2 Lower “Universal Lower Part” Version 4.2
• Gearbox V2 Lower “Universal Lower Part” Version 4.3 MTW

You can find them HERE.

3D printing parameters

• Approximate print time: ~2 h (extended V2.5 design)
• Recommended material: PLA+ or PETG (DMR rigidity)
• Layer height: 0.10 mm
• Infill: 75–90 %

Manuals

Specific SR25 DMR V2.5 installation manuals are available in the Manuals section of the website or on the project’s Discord server.