Geissele Reaction Rod


If you service or build your own AR type weapons, the Geissele Reaction Rod is a must have tool and an extra set of hands.

Up until about a year ago, I exclusively used a Derlin action block much like the one seen here. Derlin blocks are useful but introduce other issues such as setup time, lining up pins, torque flex, etc. I often found the need to apply more than mil-spec torque to the barrel nut when installing a barrel and could visually see the upper flexing. It made be cringe but I didn’t know of any other option.

I was browsing Rainier Arms’ new items section one-day and saw the Geissele (pronounced Guys-el-lee) Reaction Rod and thought; I got to try one of these.

The Reaction Rod is a very simple, solid one-piece rod of 4140 Chrome Moly steel with lugs that slide into the barrel extension and provide a solid base to work on your AR upper or barrel. You can hold a complete upper assembly, or just a barrel solidly with the Reaction Rod held in a vice without the need for plastic clamps and support rods.

Using the Reaction Rod requires a sturdy vice mounted to a solid surface. An AR upper slides onto the rod until the locking lugs engage with the barrel. There is no need to remove optics, BUIS or accessories. The locking lugs on the barrel provide all the holding power you need to assemble, disassemble or service the complete upper assembly.

The Reaction Rod allows you to rotate the upper 360 degrees around the bore axis as well as hold the work anywhere between vertical to horizontal. I was able to complete an upper build, including installing the forward assist, dust cover, gas system, free float rail and muzzle device.

The rod makes the job easy, clean and simple. There is no need to unclamp, reposition and then re-clamp a clamshell holder either. The Reaction Rod is truly an extra pair of hands. Being able to install things like optics, BUIS and other accessories is simple with the rod, just slide it on and go.

I have been using the AR-15 rod for 8-months and just acquired the AR-10 rod when I began building AR-10’s. I love the universal design that allows me to use it with any upper regardless of the design.

A couple of things to consider, first you will need a good quality vice as the rod take a lot of torque and transfers it to your work surface. Second and most important, if you use the rod to remove a stuck flash-hider, be aware that all of the torque used to loosen the flash hider is being transferred to the barrel extension and may loosen the extension rendering your barrel useless. I have only had this happen once on a very cheaply made barrel, just be aware.

If you find yourself working on your AR often or build AR’s, this is an essential tool in my book. The Geissele Reaction Rod can be purchased online at Prices range from $99 to $199 depending on the version.