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Benelli M4 -- ARGO Plugs


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I mean take the plugs themselves apart.


I was waiting for this. No, I've never taken them apart. The USMC manual says not to and that is good enough for me.


The only reason I see to disassemble them would be for cleaning. Since the pistons stay squeaky clean I'd imagine the plug does as well.

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Gave it a try tonight. Fully disassembled the ARGO plugs and cleaned them up. They are pretty filthy in there. I took some pictures for a pictorial for posterity.


Be advised, this job requires some specialized tooling to get it apart and reassembled. Also, the spring inside of the unit is heavily greased. So users soaking parts should be wary of degreasing the assembly.


I went through no less than thirty Q tips and a few pipe cleaners before the ARGO plug body was clean.

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Disassembly Guide for the Benelli M4 ARGO Gas Plug.


*Note. Most users will never need to perform this maintenance operation. The ARGO system is self cleaning and is designed to limit the amount of carbon that can build up within the ARGO gas plug. This informational is mainly for users who are troubleshooting a problem, clean up after submersion in salt water, or stripping the assembly down for coating or performing a high round count tear down, ie: 10,000 round break down. Typically, this is a task only performed by an armorer.


The ARGO plug is composed of six parts;

#89 -- Gas Plug O-Ring

#90 -- Gas Plug

#91 -- Gas Plug Pin

#92 -- Gas Plug Cap

#93 -- Gas Plug Spring

#94 -- Gas Plug Spacer


The ARGO plug itself is a relatively simple design. The Gas Plug Cap, Gas Plug Spring and Gas Plug Spacer are held into the Gas Plug by the Gas Plug Pin. The Gas Plug Pin is a solid pin that has milled ends that act as an alignment guide to prevent the pin from coming out on its own. The cap, spring and spacer under spring tension when held into the body of the gas plug. In order to remove the Gas Plug Pin, tension must be removed from it.


To remove tension from the Gas Plug Pin, I used a Magnabit 080-430-435WB Ruger Clamp Screw Bit. This bit is notched in the center and allowed the outer edges of the bit to pass around the Gas Plug Pin and seat against the Gas Plug Spacer. I then placed the Gas Plug assembly and the bit into a vice and gently squeezed the bit and the Gas Plug together. I watched the Gas Plug Pin carefully to see when it began moving. Once the spring's tension was removed from the pin, the pin centered in the hole and was driven out with a Starrett drive punch.


The assembly was then removed from the vice. The bit is a very tight fit, so it will take some effort to pull the bit free. Once removed, the Gas Plug Cap, Gas Plug Spring and Gas Plug Spacer will pull out easily. These parts will be extremely dirty. I recommend soaking the parts in solvent for a while before hitting the parts with a wire brush. On my assembly, I used no less than thirty Q-Tips to clean out the carbon inside the body of the Gas Plug. You will also notice that the spring is coated by some sort of heavy grease.


After you have cleaned the parts, it is time for reassembly.


Apply grease to the Gas Plug Spring. Insert the greased spring into the Gas Plug Cap. Insert the Gas Plug Spacer into the Gas Plug Spring. Seat these three parts into the Gas Plug. Re-installing the Gas Plug Pin can be difficult since you need to compress the spring. I found the best way was to simply get the pin started. To do this, put the Gas Plug on a hard work surface. With a punch, press firmly down against the Gas Plug Spacer while pushing the Gas Plug Pin into its hole. You'll likely only get the tip in since your punch will interfere with its insertion. Take the assembly to the vice, and press the pin in approximately 80% of the way. You'll notice as you press it in, the pin will be pushed out of alignment away from the Gas Plug Spacer since it is under spring tension. Now, use the Ruger bit and insert it through the Gas Plug to compress the spring again. Squeeze the assembly in a vice until the pin aligns with the hole. Use a drive punch to tap the pin the rest of the way in to the Gas Plug and be sure it is centered. Remove the Gas Plug from the vice, and remove the Ruger Bit to remove spring tension. As tension is removed from the Ruger bit, it will transfer to the Gas Plug Pin. As this happens, you'll see the pin push out of center alignment with the hole, and press against the outer edge of the pin's hole.


Below are some pictures to help you visualize the task.


Whatever you do, do not just try to drive the Gas Plug Pin out with a drive punch without removing spring tension first. If you attempt this, you'll either break your punch, break the Gas Plug Pin or worse, damage the ARGO Gas Plug. Once you price out how much a replacement plug costs, you'll really be crying if you do that.

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Benelli M4 ARGO Gas Plug Assembly. Note the position of the Gas Plug Pin and how it is pushed to the right in the photo. This is due to spring tension.



Here is the end of the ARGO Gas Plug. You can see how the Gas Plug Pin retains the Gas Plug Cap, Spring and Spacer. The spacer is visible below the Pin.

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This bit works well, but it isn't perfect. If I was going to be doing this task often, I would modify the inner notch and make it larger so it doesn't interfere with the Gas Plug Pin when reinstalling.



Here, the Ruger bit has been tapped into the Gas Plug. The open notch is aligned with the Gas Plug Pin. The Ruger bit is seated against the Gas Plug Spacer and is ready to be compressed.

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Here is the Gas Plug Pin. Note the tapered ends on the pin. This is what holds the pin in place when the pin is under spring tension. It also means if you attempt to drive the pin out without removing the spring tension, you will cause damage.



Here's the Gas Plug with the Gas Plug Pin Removed. Years of neglect are starting to be exposed.

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1+ Nice illustration SD.


When I have disassembled the ARGO, I use "U" or 1/2-U shaped compression punches that are easily fabricated for the task at hand. The need to use such punches to compress a spring in order to install / remove a retaining pin is pretty common in gun assemblies.

Use either a full brass punch that has the correct diameter required, or the Brownell style screw on tips that come in Delrin, brass, aluminum etc......all of which are easy to shape to the dimensions necessary.


In the case of the ARGO, I use the same punch fabricated for compression of a Mossberg 500 spring.





Edited by benelliwerkes
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You have some great tools Benelliwerkes. I may copy many of these when I get my mill.


By the way, have you ever removed and reinstalled the Ejector Frame? It appears to be riveted in place. A project I'm working on requires that I strip everything off the barrel. My other concern is for the detent and spring that ratchet on the magazine cap. Is that removable?


I don't even have a M4 barrel on hand at the moment to assess the task.



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My other concern is for the detent and spring that ratchet on the magazine cap. Is that removable?




Short answer is NO, I have not removed that part either....I believe they are pressed into place, like most other manufacturers assemblies. I'll take a close look later today.



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