PolarStar JACK + MAXX MODEL alignment kit for SR25 DMR

Version 2.5 of the hop-up alignment system, specifically designed for SR25 DMR HPA (Designated Marksman Rifle) replicas with a long V2.5 gearbox.

• PolarStar JACK engine (compact HPA engine for AR-10/SR25 platforms with excellent response in DMR configurations).
• MAXX MODEL chamber (high-precision hop-up chamber optimized for DMR builds using heavy BBs).

This kit ensures perfect alignment between the JACK nozzle and the MAXX MODEL chamber in long V2.5 gearboxes, eliminating play and improving consistency at the extended ranges typical of DMR builds. Compatible with ICS lowers and split systems for SR25 platforms.

Compatibility

Component	Compatibility
HPA Engine	PolarStar JACK SR25
Hop-up Chamber	MAXX MODEL
Base Replica	SR25 DMR
Gearbox	Long V2.5 / ICS SPLIT

What the kit includes

• Reinforced rear clip for mounting on a long V2.5 gearbox via rear pin or fixed stock.
• Extended base with housing for M3 inserts (optional brass).
• Side clip for routing the JACK HPA tube/line.
• Front locking top cap optimized for the MAXX MODEL chamber in SR25 platforms.
• Rear plate with mounting point for an M5 screw (extra reinforcement for DMR builds).

V2.5 adaptation: This kit features extended dimensions and specific reinforcements for long V2.5 SR25 gearboxes, maintaining the same alignment logic as V2.1 but with greater stability for heavy BBs (0.32g+).

Installation and adjustment

1. Printing and preparation

   • Print the parts with 70–85% infill (extra reinforcement for DMR builds).
   • Lightly sand the internal areas for a clean fit, especially on the extended base.
   • Apply dry lubricant on contact surfaces to make future adjustments easier.

2. Installation in the replica

   • Insert the extended base into the ICS lower and secure the M3 inserts.
   • Install the rear clip aligned with the rear pin of the long V2.5 gearbox.
   • Install the MAXX MODEL chamber with the long DMR inner barrel; the top cap locks the assembly while keeping everything centered.
   • Route the PolarStar JACK HPA line through the reinforced side clip.

3. Final fixation

   • Secure the rear plate using an M5 screw and large washer for maximum rigidity in DMR configurations.
   • Verify that the JACK nozzle enters the MAXX MODEL chamber perfectly centered with no lateral play.
   • Adjust the JACK pressure (80–120 PSI recommended for DMR) and test feeding with heavy BBs.

Required components (not included)

• 6× M3 × 4.2 mm inserts (one extra due to the long gearbox).
• 6× M3 × 8 SHCS screws (additional reinforcement).
• 1× M5 × 16 mm screw + washer (for the rear plate).

Lower receiver recommendations

Compatible with original ICS metal lowers for SR25 DMR.
For printed builds, these Gearbox V2.5 Lower “Universal Lower Part” models work perfectly:

• Version 3 (adapted for long gearbox).
• Version 4.2 (extendable).
• Version 4.3 MTW (reinforced).

You can find them HERE.

3D printing parameters

• Approximate print time: ~2 h (larger parts due to V2.5).
• Recommended material: PLA+ or PETG (for greater resistance in DMR builds).
• Layer height: 0.15 mm – 0.20 mm
• Infill: 70–85% minimum.

Manuals

Installation and adjustment manuals for SR25 DMR are available in the Manuals section of the website or on the project’s Discord server.

Related products and articles

Similar product designs:

• PolarStar F1 + MAXX MODEL alignment kit for SR25 DMR
• GATE Pulsar-H + MAXX MODEL alignment kit for SR25 DMR
• GATE Pulsar-S + MAXX MODEL alignment kit for SR25 DMR

Technical articles for this topic:

• MAXX Model Hop-Up: Differences Between Models, Versions, and Compatibility with HPA Kits
• Polarstar F2 Nozzle: Length Guide, Compatibility by Model, and How to Order a Custom Fit