Geissele Reaction Block for AR-15/LR-308 - Mil-Spec Buffer Tube Diameter

The Geissele Reaction Block for AR-15/LR-308 is a gunsmithing workbench tool designed to stabilize your lower receiver assembly during build and maintenance. If you're assembling an AR platform rifle or performing lower receiver work—whether you're a professional armorer or a serious home builder—this block keeps your receiver locked in position while your hands stay free to tackle trigger work, buffer tube installation, buffer retainer nut seating, and other critical assembly tasks.

Built around a mil-spec buffer tube diameter design, the Reaction Block accepts your assembled lower and buffer tube, then clamps the whole setup at multiple contact points (12, 3, 6, and 9 o'clock positions). Simple nylon screws handle the clamping; loosen them, rotate your lower to the next orientation, and you're working at a new angle without breaking down the assembly. This modularity saves time when you're threading fasteners, fitting components, or inspecting fitment from every side.

The appeal is straightforward: a rock-solid platform means cleaner work, fewer fumbled parts, and less frustration on the bench. Whether you're building one rifle or running a small shop, keeping both hands free—one holding your tool, the other guiding the component—transforms lower receiver work from awkward wrestling match to controlled operation. The Geissele Reaction Block is the kind of tool that pays for itself in time saved and quality gained.

Key Features

• Multi-position clamping at 12, 3, 6, and 9 o'clock orientations for flexible access to all receiver surfaces
• Compatible with mil-spec buffer tube diameter for AR-15 and LR-308 platforms
• 90-degree rotation increments without removing the buffer tube assembly
• Frees both hands for tool operation and component handling
• Nylon screw clamping mechanism for secure, non-marring hold
• Engineered for lower receiver operations including trigger work, buffer retainer nut installation, and general assembly tasks

Specifications

Frequently Asked Questions

Will the Reaction Block work with my AR-15 lower and buffer tube assembly?

Yes, provided your buffer tube is mil-spec diameter. Slide the assembled lower and buffer tube into the block at any of the four contact points, tighten the nylon screws, and you're ready to work.

Can I use this for LR-308 (DPMS-pattern) rifle builds?

Yes. The Reaction Block is designed for both AR-15 and LR-308 lower receivers that use mil-spec buffer tube diameter.

What tasks can I perform with the lower clamped in the Reaction Block?

The block is designed to support lower receiver assembly operations, trigger installation, buffer retainer nut installation, and other work requiring hands-free stability. Always verify the block provides adequate support for your specific task.

How do I change the angle of the lower without removing it from the block?

Loosen the nylon screws, remove the lower and buffer tube assembly, and reinsert it at the next desired orientation (90-degree increments at the marked positions). Tighten the screws to secure it in the new position.