Geissele Reaction Rod

Geissele Reaction Rod!

As many readers know my family and I have a cattle ranch in the highlands of central New Mexico. In order to effectively manage our herds and mitigate calf mortality, coyotes and other predators must be culled. Aside from coyotes…there has been a recent surge in cattle theft across the Western States. The idea of coming across cattle thieves armed with a scoped 30-06 hunting rifle personally does not sit well with me. Usually when I go to the ranch I have at least a handgun, but with the rise in cattle theft a Smith and Wesson M&P15, accompanied by a handful of standard capacity (30 round) magazines, has been my primary ranch companion.

My Primary ranch rifle.

My Primary ranch rifle.

My M&P-15 started life out as an M&P-15 Sport.  What attracted me to the Sport was the fact that the rifle featured a 4140 1/8 twist 5R (5 Groove rifling) barrel. Having a 1/8 twist barrel offers me the versatility to shoot 52 to 77 grain bullets. The gun easily groups about ½ MOA with Hornady Match 75 grain BTHP’s and will hold about 1 MOA with Federal 55 grain XM193. Borrowing from its sister brand, Thompson/Center, Smith and Wesson incorporated 5R, or 5 groove rifling. 5 groove rifling incorporates 5 grooves and 5 lands as opposed to the traditional 6. The theory is that the bullet experiences less deformation while going down the barrel and will experience an increase in velocity due to a less steep angle between the land and groove. This gentle angle theoretically lets less gas around the bullet while the bullet is still in the bore.

Is there less deformation and more velocity with a 5R barrel? An upcoming article will explore this question in greater detail.

M&P 15 without forward assist or dust cover.

M&P 15 without forward assist or dust cover.

The rifle has been highly modified. I added a Troy MRF-R 12” to utilize a more contemporary firing grip on the rifle as well as have a place to mount a flashlight and a bipod. I added a Magpul MOE pistol grip, as well as a B5 SOPMOD stock. I store small vital components in the stock and grip: CR123 batteries, gas rings, extractor/extractor spring/O ring, spare firing pin, and the front sight adjustment tool that came with my Magpul MBUS front sight. I also run a Magpul B.A.D lever. Smith and Wesson used 7075 T6 Type 3 Hard Coat Anodized aluminum for the lower and upper receivers. They chromed the gas key and the bolt carrier. The gun comes with the standard carbine length gas system. I am extremely pleased with the rifle and after several thousand rounds of Federal XM193 the rifle has never had a malfunction. My only complaint about the rifle is that it does not come with a forward assist or an ejection port cover assembly/dust cover.

Enter the Geissele Reaction Rod.

A quick call to Bravo Company Manufacturing and I had a stripped upper receiver, a forward assist assembly, and an ejection port cover assembly. Though I have swapped many barrels and rebuilt many upper receiver assemblies, it is a task I loathe. Traditionally I have used the clamp method, in which the upper receiver is pinched between a Model 1 upper receiver block, then tightened in a vise. This method can put a lot of stress on the upper receiver, mar the hard coat finish, or even break the receiver index pin on the barrel (Something I have seen happen….which can be fixed by a competent welder). I was not looking forward to swapping the upper receivers until I came across the Geissele Reaction Rod while surfing around the MilitaryTimes/GearScout blog. Intrigued, I ordered the Reaction Rod from the Geissele Automatics Website.

 The Geissele reaction rod requires a heady duty vise to work properly.

The Geissele reaction rod requires a heady duty vise to work properly.

The Geissele reaction rod is made of 4140 Chrome moly steel. The rod securely holds an upper receiver by interfacing with the barrel extension on a standard Ar15/M16 barrel. The rod is precision fit to the upper receiver and there is ABSOLUTELY NO WOBBLE between the rod and the upper receiver. Aside from being used to tighten the barrel nut on an Ar-15/M16, the rod can be used to install/remove flash hiders and muzzle brakes, attach scopes and accessories, and for general maintenance.

Torquing on a Vortex Viper PST 2.5-10.

Torquing on a Vortex Viper PST 2.5-10.

The Geissele Reaction Rod is an amazing product! Removing the barrel from my M&P-15 was extremely easy. After tightening the rod to the vise, I slid the receiver onto the rod and aligned the receiver index pin to the receiver. I  hand-tightened the barrel nut and was pleasantly surprised how little energy it took when my torque wrench clicked to indicate that the barrel nut had reached the required 80ft/lb. of torque. Rotating the upper receiver on the rod 180 degrees, I installed the forward assist. Another 90 degree turn and I installed the ejection port cover assembly. Adjusting the rod perpendicular to my workstation, I reinstalled the gas tube, Troy hand guard, and the Vortex PST riflescope.


Final thoughts.

The Geissele reaction rod is a product that armorers in the industry have sorely needed. The engineering, manufacture and finish of the product are excellent, and exactly what you would expect from Bill Geissele. Armorers should note that this product will require a very strong and securely attached vise. If you are not an armorer and have no desire to swap barrels and build upper receivers, you can still utilize this tool for installing forearms, gas blocks, back-up sights, accessories, and muzzle devices. I can’t wait to use this product again.

Do you have any experience with the Geissele reaction rod? Tips, questions and gripes are welcome in the comments below.

Load that bipod! Stay safe!

John Noveske 1976 - 2013. Rest in Peace amigo.

John Noveske 1976 – 2013. Rest in Peace amigo.



Thomas Gomez

Thomas Gomez currently resides in the mountains of central New Mexico. He has an M.B.A, an Ar-15/M16/M4 armorer certification from Specialized Armament Warehouse as well as a Glock armorer certification. Aside from writing for The Firearm Blog he works as a Clinical Analyst for a large Hospital. He spends his free time farming, ranching, hiking, fly-fishing and hunting in the beautiful forests and prairies of New Mexico. He can be reached at


  • Very good idea! Now I wish some one made something along the same lines for building ak kits. Thomas,your write up about carrying a AR around the ranch stuck home with me. I too live on a ranch(180ish acres). But I carry my 5.45 SGL AK with me with a 4x psop scope and my tokarev. Granted,being in central Texas and mostly raising sheep and goats I don’t have to be worried about thieves,but coyotes/wild dogs and hogs will do a number on a goat and sheep herd. And there is always the threat of armed illegal immigrants being around. But this is my point:I honestly don’t know a farmer who carries a lever action or shotgun around anymore. Every one carries a AR15/10,sks,or ak. These rifles really do have a place as “the modern day musket”. Maybe it is a good thing,maybe it is a bad thing we have to carry these around on our own property. But it still stands,they are the new bottom line in farm rifles now. And thanks again for such a good review.

    • Thomas Gomez

      @Rich Guy

      Thank you for the feed back. That 5.45 SGL is a nice rifle! Love the sound of those ak’s when the shoot. What kind of groups do you get with that 4x at 100 yds? I know Hornady is making a 5.45 round. Have you gotten a chance to run some through your rifle? I am glad you are well armed on your ranch. At the end of the day we are ultimately responsible for our own security…

      • Well on my best day it was a 1 1/2 5 shot group at 100yrds with Hornaday,but I think the shooting gods where smiling on me that day as that is not the norm. On average I get about a 2 1/2-3 inch group with Hornaday. But what is strange is that it does not open up at longer ranges like you think it would. I have taken it out to 500 yards once with my friends 6x scope(Nikon I THINK),and got a 14 1/2 inch grouping.Terrible for a AR,but not bad for sheet metal and rivets. The furthest I have taken a coyote is at 218yrds,and with a single shot(also Hornaday). But I mostly run Bear ammo through it for fun shooting.

        • Thomas Gomez

          I will admit it is hard to group 1 MOA with a 4 x scope. I was testing out a Leatherwood CMR on a rifle that I knew was a sub-MOA gun and the best I could do was about 1.75 MOA. Hope this finds you well. Thank you Sir for the feedback.

  • Lord Cthulhu

    This is not the optimal method of securing upper receiver for any work where the barrel nut is involved. Contrary to author’s claims, it DOES put additional stress on the receiver extension index pin and the upper itself when the barrel nut is tightened.

    Think about it: you are fastening the barrel nut to the upper receiver. These are the two parts that torque needs to be applied to for that nut tightening action to occur. If you don’t use the traditional method (the upper receiver clamped in the vice using a receiver block), and instead fix the barrel extension in the vice by using this tool, then the barrel extension would have to transfer full torque that you apply to the barrel nut wrench (up to 80 ft-lbs) to the upper receiver through that little index pin and square notch cut in the receiver (made of aluminum alloy)! Not a good idea.

    This simply CAN’T HAPPEN HAPPEN when using the traditional method (upper receiver clamped in a action block) as there is very little to no torque applied to that pin when tightening the barrel nut. All interaction is between the upper receiver and the barrel nut, the barrel extension simply sits in between. Yes you might mar the finish. Oh the tragedy.

    This “reaction rod” could be suitable for working with muzzle devices though: it would put zero torque on that pin when you tighten the muzzle brake. But clamping the barrel in a barrel block works just as well. Or stepping on the FSB, for that matter 😉

    • thatguy

      want to try that again? Form the Geissele website…

      “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.

      The Geissele Reaction Rod is machined at Geissele
      Automatics’ state of the art manufacturing facility in Norristown,
      Pennsylvania. 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

      • Lord Cthulhu

        Yes let me try that again: Geissele, please stick to making excellent triggers rather than marketing snake oil.

      • vereceleritas

        I’m going to have to agree with Cthulhu on this one. Securing an upper to a vice by interfacing only with the barrel extension is going to put more stress on the index pin when you torque the barrel nut, not less. I love Geissele’s products but I think they got it backwards on this one. Should be great for FSB and muzzle device work though.

        • Thomas Gomez

          Thank you for the response and reading my article!

      • RocketScientist

        Cthulhu is correct. The Geissele website can say whatever it likes, the simple laws of mechanics say otherwise. Drawing a free-body-diagram of the three-member system comprising the barrel/extension, the reciever, and the barrel nut make what Cthulhu is saying clearly true. An attempt to describe the relationship in wirting: As you apply torque to the barrel nut, it attempts to rotate and once snugged up this angular (rotational) motion is resisted (via the engaging threads) by the upper receiver. If the receiver is instilled in a typical clamshell vise block, the applied torque is transferred through the receiver into the vise-block, to the vise, to the workbench, etc. If instead the Geissele Reaction Rod is used, the torque must be transferred from the receiver to the receiver index pin on the barrel extension, to the Reaction Rod, to the vise, etc. In the first instance (using the common clamshell vise block) the barrel/extension see no torque (and hence no stress applied to the receiver index pin) and is simply compressed between the receiver and the barrel nut. When using the Reaction Rod, ALL off the torque passes through the barrell/extension, placing significant shear stress on the pin and tear-out stresses on the cutout in the receiver. Conversely, when applying torque to the barrel itself (muzzle device installation, etc) using a clamshell vise-block puts the stress through the index pin, while using the Reaction Rod would keep it stress free.

        • Thomas Gomez

          Hello Rocket Scientist! What is your take on the way the military swaps their barrels via the barrel clamp method? What kind of rifles do you like building? SBR’s? Recces? Precision? Thanks for the feedback!

      • Thomas Gomez

        I take it you have a Geissele rod and like it? What are your experiences with the device?

    • JCM

      This not a revolutionary concept: there is a Brownells tool that does pretty much the same thing for 20 bucks less.

      I wouldn’t use it for barrel installs either. Get a vice block for that.

      • Thomas Gomez

        Hello JCM. Thank you for the feedback. I saw the Brownells one and your are correct in your statement. Bill Geissele was inspired to build this tool by seeing something very similar at a military installation. I believe HK has something similar for the HK 416 barrel and receiver. The Brownells tool requires a driver and I don’t think it interfaces as well with a viSe as the Geissele. Hope this finds you well!

    • Thomas Gomez

      “Stepping on the front sight base!! ” Too funny! Thank you for the feed back sir. According to the Army Technical Manual TM9-1005-319-23, the manual advises that the armorer pinch the barrel in a barrel vise and then apply the required torque…30 – 80 ft/lbs. Since the Geissele rod essentially “grabs” the vice from the barrel extension don’t you think the Geissele rod is simply mimicking the barrel vise…? Just interfacing in a different part of the rifle? I look forward to your response. What configuration of ar15’s do you like to build?

  • Dave

    I own clam shell and DPMS upper receiver block. I don’t use them anymore.

    I use a Geissele Reaction Rod and it works great. Plain and simple. I’ve had barrel nuts so fricking tight they were flexing the upper receiver in a clam shell. Reaction Rod worked perfect. If you are generating so much torque that your index pin is screwing up your upper receiver, you’re over torquing it.

    • Thomas Gomez

      Hello Dave! Thank you Sir for the feedback. After using the Geissele rod I will never use my clamps again. I have used the clamp method for the last 7 years and as soon as I used the Reaction Rod I was sold. Hope this finds you well!

    • I’ve had the same experience and also use the Geissele Reaction Rod. Never a problem and it is significantly easier to do a barrel swap.

  • INKev

    The author writes “when my torque wrench clicked to indicate that the barrel nut had reached the required 80ft/lb. of torque.”

    isn’t 80 pounds the MAXIMUM you should be torquing? I normally go to 30 lbs and then tighten only enough so the tube clears the next hole (making sure it isn’t over 80 lbs).

    • Garrett

      Yea, I’ve always done a 30 ft-lbs pre-load, backed off the nut, then another 30 ft-lbs. I then check for gas tube alignment. I’ve heard from some people that 30 – 70 ft-lbs is the range for torquing. This is the first I’ve seen 80.

      • Jordan Bear Pollard

        I’ve been told that 80 is the maximum, however, moving towards the high end of the spectrum can adversely affect accuracy. I’ve never seen it in practice, but my thinking is that it’s simply an issue of opinion and owner preference.

    • Thomas Gomez

      INKev. You are correct Sir. I should have made the article clear. I had to go all the way up to 80 ft/lbs to get the barrel nut to align perfectly. I was simply amazed at how easy it was to torque all the way to 80 ft/lbs. Thank you for catching that.

  • Thomas Gomez

    You need the Dos Equis guy as your avatar! lol

  • Thomas Gomez

    Vise! Vise! Vise! Vise! Going to skip recess and write that on the chalk board several hundred times…as Brandon Webb says…perfection does matter. Thank you Sir for reading my article. Hope this finds you well!

  • Your mom likes my AR-15

    Farmboy762… Love the article. Recently took an armorers class, the instructor was also using the geissele rod and spoke very highly about it. I plan to get one when geissele has them in stock. Take care and thanks for recommending the geissele rod!! Good day sir!! You are a scholar and a gent!!

    • Thomas Gomez

      Love that screen name!

  • MrCaveman68

    No where in the article did the author say that the reaction rod would not apply stress. He did mention absolutely no wobble between the rod and the upper receiver. He also mentioned that the standard clamp method applied stress to certain components enough so that they may break, but again never mentioned that the same is either true or untrue of the reaction rod. So why all of the criticism, he is merely suggesting an easier way to do things, stop trying to make a lier out of him when he didn’t say it. Read the article again if you didn’t understand it the first time.

    • Thomas Gomez

      Thanks for the feedback MrCaveman!

  • GmanJynx

    I just recently finished a armorer certification class taught by a retired military armorer of 26+ yrs. The instructor showed both the reaction rod and the vise block methods for any and all types of work on an upper reciver. The instructor had nothing but good things to say about the reaction rod and had never had a malfuntion (snapped indexing pin) in all his time using one (hundreds of builds / barrel swaps). I have to say I am planning on buying one myself for my tool kit. I tend to agree with Dave that if you are generating that much torque to snap the pin your are either the Hulk of had a faulty pin. I do not understand the attacks on the author for voicing an opinion on a tool that he was impressed with. Keep up the good work Thomas.

    • Thomas Gomez

      Thank you Sir. Congratulations on your recent certification!