HPA Adapter M870 Breacher Shotgun to M4

A plug and play HPA adapter that converts compatible M870-style gas shotguns to use an external HPA system with Airsoft M4 AEG magazines.

Product Features:

• Compatible with TM M870, Breacher, Golden Eagle and Secutor style gas shotguns.
• Compatible with most Airsoft M4 AEG magazines.
• Plug and play design with valve, feed lips and gas router pre-installed.
• No donor parts or assembly required.
• Injection moulded polycarbonate M4 magazine well.
• Polished internal magazine well for smoother magazine insertion.
• Adjustable side shims reduce magazine wobble.
• Reversible side shims provide additional adjustment for wider magwells.
• Rear adjustment screw reduces vertical movement of the adapter.
• Integrated BB retention system minimises BB loss during magazine changes.
• Swappable rear magazine shim included.
• Recommended operating pressure: up to 150 PSI maximum.
• Supplied with a US Foster HPA fitting.

The AIRTAC M870 Breacher Shotgun to M4 HPA Adapter converts compatible M870-style gas shotguns to operate from an external High Pressure Air system while feeding from Airsoft M4 AEG magazines. Designed for TM M870, Breacher, Golden Eagle and Secutor style platforms, it provides increased ammunition capacity and faster reloads without requiring permanent modification to the shotgun.

Supplied fully assembled, the adapter includes the valve, feed lips and gas router already installed, allowing it to be fitted straight from the box without transferring components from an existing gas reservoir. The injection moulded polycarbonate magwell features polished internal surfaces to promote smooth magazine insertion and reliable operation.

To improve fitment across different shotgun manufacturing tolerances, the adapter incorporates adjustable side shims and a rear adjustment screw. The side shims can also be reversed to provide additional adjustment for wider magwells, while the rear screw reduces vertical movement within the receiver. An integrated BB retention system helps minimise BB loss during magazine changes for more efficient reloading during gameplay.

Designed for compatibility with most Airsoft M4 AEG magazines, the adapter is supplied with a US Foster HPA fitting and should only be operated with a regulated HPA system at a maximum pressure of 150 PSI.

Range Overview:

AirTac’s HPA Adapters range converts traditional gas-powered replicas to use high-pressure air magazine systems with seamless reliability. Designed for multiple replica platforms, each adapter features precision-moulded construction, a secure BB-retention system, and standardised US-thread fittings for broad compatibility. The range combines rugged strength with practical installation, giving players smoother reloads and extended playtime through improved air efficiency and modular flexibility.

• Injection-moulded polymer housings provide durability and consistent alignment
• Standard US-thread fittings ensure cross-system HPA compatibility
• Integrated BB-retention systems prevent feed loss during reloads
• Supplied with magwell inserts, screws and shim sets for precise fitment
• Available for multiple pistol and SMG platforms for modular loadouts
• Engineered for reliability, consistency and long-term performance

Brand Statement:

AirTac specialise in developing high-performance HPA conversion systems for airsoft enthusiasts seeking consistent, efficient, and adaptable performance. Their focus on precision engineering and robust construction ensures every product delivers dependable field use, intuitive function, and lasting value.

Safety Information:

Do not exceed 150 PSI when operating any airsoft HPA adapter Always use air regulated by a secondary regulator Check PSI output before connecting air to the adapter Do not connect directly to unregulated air sources, CO2 systems, or high-pressure tanks Do not use with incompatible high-pressure air lines or fittings Always ensure correct setup and operation before use