Geissele Reaction Block | AR15/M4 Milspec

The Geissele Reaction Block for AR15/M4 platforms is a tool designed to assist with lower receiver assembly and maintenance. Compatible with mil-spec buffer tube configurations, it provides a stable interface for securing the lower receiver during various armorer tasks. The design allows the receiver to be positioned at multiple orientations, supporting improved access to components during installation or adjustment.

This block enables users to reposition the lower receiver in 90-degree increments by loosening the integrated nylon screws and re-seating the receiver. Its construction is intended to provide consistent support while allowing hands-free operation during tasks such as buffer tube installation and related procedures. The Reaction Block is suitable for use in both professional and personal gunsmithing setups.

Specifications

• Compatibility: AR15 / M4 platforms (mil-spec buffer tube only)
• Application: Lower receiver assembly and maintenance
• Receiver Positioning: 12, 3, 6, and 9 o’clock orientations
• Adjustment: 90-degree incremental rotation
• Retention System: Nylon screws
• Function: Supports hands-free operation
• Use Case: Buffer tube installation and general armorer tasks