A Hot Rod for the AR builder

You probably know Geissele as a maker of really good triggers for AR-15 and M16 series rifles, but the Norristown, Pennsylvania firm been expanding their product line, and they’ve created a gunsmiths’ tool that is a must have for anyone that does mid-range work on AR-type weapons, especially work that involves removing and replacing barrels.

We’ve lost count of the number of barrels we’ve R&R’d and we’re not even gunsmiths here (although maybe there’s an armorer’s school or two in the immediate future). With the existing tools — we use an action block from Brownell’s — you have to take extreme care not to make a mess of things. Plus, different action blocks are optimum for different types of upper receivers. We’re doing lots of prototype and retro AR builds lately, so we have the delicate carrying-handle uppers that were used from the Hollywood and Costa Mesa prototypes through millions of M16A1s and SP1 civilian rifles. You need an action block that accepts the carrying handle — which is not ideal for a flattop receiver. So that’s two sets of action blocks.

And we’ve lost count of the number of AR’s we’ve seen that had barrel work done by Bubba with tools (identified by their witness marks) ranging from bare metal vises (ouch) to pipe wrenches. Upper receiver damage has included twisted uppers, broken carrying handles (usually through the accessory/scope/deflector mounting hole), crushed receivers that are sprung enough to cause interference with the bolt carrier group, broken-off threaded sections and stripped threads. And that’s only the structural damage: for every structurally damaged receiver Bubba leaves behind, he “merely” wrecks the cosmetics on a dozen more.

Some of these parts are historic and irreplaceable, and Bubba’s been going through them like Staten Island looters going through a convenience store. Not good.

So the best answer, till now, has been the action block; but the above-mentioned limitations are never far from a gunsmith’s or armorer’s mind as he tries to remove an overenthusiastically seated barrel nut.

Enter the Geissele Reaction Rod, which Is a reconceptualizaton of the action block idea: an internal mandrel, made of steel, that holds the upper receiver and mates firmly with the locking lug recesses in the barrel extension. This means when you chuck the Reaction Rod in your vise, add the receiver, and then bear down on the barrel nut, all of the torque you’re applying is not putting torque on the upper. The vise is not under any circumstances compressing the upper. This thing needs to be in your tool box if you wrench on ARs — period. Here’s the website blurb:

The Geissele Reaction Rod is a tool that securely holds an upper receiver assembly for maintenance and assembly work.  It will make working on an AR15 or M4 carbine a dream.  The removal and installation of barrels, flash hiders, gas blocks and hand guards is made much easier and simpler.  The Reaction Rod is designed to be gripped in a bench vise so that the rod is either horizontal or vertical.  The upper receiver is then slid onto the rod and the rod’s integral splines enter the barrel extension and secure the barrel extension from turning.  This allows all the torque from barrel nut wrenches to go directly into the barrel extension.  In contrast, receiver vise blocks transmit the turning force into the aluminum receiver, a good part of which passes through the small, easily distorted receiver index pin.  With the Geissele Reaction Rod, marring of an upper receiver’s finish by gripping and twisting inside vise blocks is eliminated and so is the need to remove sights and mounts from the receiver’s M1913 rail.

Heh. Until reading that we hadn’t even thought about that possible benefit. Because in most circumstances the optics come off before the rifle goes on the bench… it’s not like your zero’s going to survive a barrel changes. But we can see a few common tasks where leaving the glass on and still holding zero would be nice. Flash hider replacement is one (we usually use a front sight base block, also from Brownell’s, for that). Finally, a couple of words on how they make it:

The rod is cut from a solid bar of 4140 Chrome Moly steel, properly quenched/tempered and ground to an exact diameter that is smooth and straight so the rod will enter an upper receiver without wobble.

via Reaction Rod.

The Reaction Rod will set you back $59 plus shipping from Geissele. Brownell’s has had for some time a somewhat similar-looking fixture, but we’re not sure what it’s made of (and Brownell’s isn’t telling). We suspect plastic, which is the wrong stuff for this job. It also looks shorter than the Reaction Rod. It is, however, cheaper, and that’s something.

And, oh, yes: their triggers are the heat, too.