The Geissele Automatics Reaction Block (brand part no. 05314) is a steel fixture built to aid AR15/M4/M16 lower receiver assembly. Made by Geissele Automatics, a name best known for match-grade AR triggers, the block lets an armorer slide a lower receiver in at the 12, 3, 6, or 9 o’clock position and rotate it in 90-degree steps by loosening two nylon screws. That keeps both hands free for buffer retainer nut installation and other lower receiver work.

Key Specifications

• The lower receiver slides in at 12, 3, 6, or 9 o’clock positions once the buffer tube is installed.
• You can rotate the receiver in 90-degree increments just by loosening the provided nylon screws and repositioning it.
• It’s built as an ultra-stable steel platform, keeping the receiver locked down through a range of lower-receiver operations.
• It makes buffer retainer nut installation quick and one-handed instead of a two-person job.
• Rotating the receiver in the block keeps both hands free to work rather than one hand holding the lower steady.

Frequently Asked Questions

Does this block work before or after the buffer tube is installed? It’s used once the armorer has installed the buffer tube, at which point the lower slides into the block for further work.

Can I use this for anything besides buffer retainer nut installation? Yes, the stable rotating platform is useful for a range of lower receiver assembly and disassembly operations.

Buy the Geissele Reaction Block

A reaction block this well thought out turns a fussy two-hand job into something you can do solo. Order it from our Lubbock, Texas gun shop for fast, direct shipping, and browse our gunsmithing tools lineup.