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Benelli M4 -- Receiver Extension Removal/Reinstallation Guide


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Benelli M4 Receiver Extension Removal



This tutorial is to show how to disassemble any of the Benelli M4 receiver extensions.




There is a lot of misinformation out there regarding disassembly of the Benelli M4’s receiver extension. Benelli USA will tell you that you will destroy the aluminum receiver if you attempt to remove the receiver extension. This is false. The receiver extension is installed with a green thread locker at the factory. In my experience, this thread locker is tougher to break than even red Loctite. Heat is mandatory to break down the thread locker’s hold or you will damage the fine threaded aluminum receiver.


I would recommend the following steps be taken before you apply heat to your Benelli M4;


1. If you have tritium night sights in your rear sight, remove the aperture.

2. I recommend removing springs from your receiver and existing Receiver Extension. The application of extensive heat can damage springs.

3. Degrease your work area before applying heat to reduce smoke/fire hazard.


Source the required tools for the job;

a. Vice

b. Heatgun or MAPP Torch (Preferred)

c. 27mm Box Wrench

d. 19mm Box Wrench

e. Magna Tip Weaver Clamp Screw, 080-430-625WB

f. Punch/Pin

g. Loctite Primer 7471

h. Loctite Red 271

i. Snap Ring Pliers

j. Wire Brush

k. Oil/Grease

l. Solvent

Some of these items aren’t mandatory to have, but you’ll have a much harder time doing the install without. I found the Magna Bit Weaver Clamp Screw bit works extremely well for removing the Stock Retaining Screw. I have not found a flathead screw driver large enough to fit.





Step by step disassembly process


1. Clear the weapon of ammunition and make it safe

First off, ensure that your Benelli M4 is unloaded. Remove all ammunition from the weapon and remove it from your work area.



Edited by StrangerDanger
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2. Disassemble the weapon


Remove the barrel, bolt carrier group, trigger group and the stock. If you can easily remove the magazine tube, do so.




3. Remove the internals from the Receiver Extension

a. Use a pair of snap ring pliers to remove the Stock Retaining Ring at the bottom of the Receiver Extension.



Edited by StrangerDanger
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Side note: This is the part that gets people into trouble with their Mesa Tactical Urbino stock. Once you realize how little torque is required to remove the Stock Retention Screw from the receiver extension, it is easy to see how Locktited screws will back the Stock Retaining Screw out. The amount of torque applied is no match for the cheap snap-ring to contain.



You can see in this photo how the spring has partially ejected out of the Receiver Extension. This is due to the punch being in place. It is much more manageable this way.

Edited by StrangerDanger
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d. Contain the Recoil Spring into the palm of your hand as the punch is removed.



You can see in this photograph how long the Recoil Spring is. It's about twice the length of the Receiver Extension. The contents are under quite a bit of tension, so be careful to contain the spring when removing the punch. Expect the entire assembly to be filthy.


e. Tip the receiver back to allow the Recoil Spring Plunger to slide out of the Receiver Extension.



Edited by StrangerDanger
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4. Surface Preparation

I recommend you use a solvent to flush away all debris and oil from the Receiver and Receiver Extension at this time. I have a five-gallon bucket filled with Mineral Spirits to act as a dunk tank. I poured three gallons of odorless Mineral Spirits into the bucket. A simple plastic lid seals the content. Debris settles to the bottom. I haven’t noticed any evaporation of the chemicals in the year I have had it assembled.

You can also use a spray type solvent such as BreakFree Powder Blast or Gunscrubber.

This will reduce the chance of smoke and/or fire when heating your Receiver/Receiver Extension.





Edited by StrangerDanger
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5. Receiver Extension's Lock-nut Removal

To remove the Receiver Extension, you must heat the Receiver Extension's lock-nut with a heat-gun for approximately 30 minutes or more. A MAPP torch would also work, and be faster. After doing around two dozen of these receiver extensions, I would say the MAPP torch is the preferred method. Benelli coats the threads with a green thread-locker compound. Put the Receiver in a vice. I found the best place to clamp to is below the rear sight and upside down. You do not want to crush the Receiver with the vice. Apply just enough tension to hold the Receiver in place. Make sure you apply some padding between your Receiver and the vice. Preferably something non-flammable. Balsa wood blocks work well.


The lock nut is a 27mm box wrench. The nut is a common right-hand thread. "Rightie Tightie, leftie loosey." It is best to use a closed box wrench to reduce the chance of slipping and to apply the torque more evenly around the circumference of the lock-nut. Just slip it over the end of the receiver extension and seat it over the lock nut. You do not want to apply a lot of torque to the Receiver. You want the heat to break the thread-locker's hold. I never used more than one arm's strength to apply torque with. Once it is heated sufficiently, the nut will begin to turn slowly. Continue heating until the lock-nut is completely removed and slides off the end of the Receiver Extension.



Edited by StrangerDanger
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6. Removal of the Receiver Extension

Continue to apply heat to the Receiver Extension's threaded area. Use an open ended 19mm box wrench on the flat spots of the receiver extension to apply torque.


The Receiver Extension is also common right-hand thread. This may take another 30 minutes with a heat-gun to break the thread-locker compound's hold. The fit of the wrench on the flats of the Receiver Extension is not exactly the best. You will mar it up in the process if you try to gorilla your way through it. Let the heat do its job.



Edited by StrangerDanger
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7. Clean up and surface prep

Once the Receiver Extension unscrews, clean up the threads of the Receiver with acetone or another solvent. A wire-brush will help. If you want overkill, use Locktite primer on the threads of the Receiver, the lock-nut and the new Receiver extension.





Edited by StrangerDanger
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8. Receiver Extension Re-installation

To reassemble, I highly recommend that you apply Red Locktite 271 to the Receiver Extension at this time. Screw the new Receiver Extension in so that the threads are flush with the inside of the Receiver. If you thread the Receiver Extension too far into the Receiver, you will not be able to install the collapsible stock's pistol grip portion. The pistol grip threads onto the external threads of the Receiver Extension near the lock-nut. You'll notice that you can thread the Receiver Extension into the Receiver all the way by hand. The only thing that really retains the Receiver Extension is the thread locker and the lock-nut.


I recommend rinsing the Receiver and the Receiver Extension in a solvent to make sure all surface debris and oil has been removed. I recommend using a wire brush to clean up the threads. Continue flushing the mating areas with solvent to make sure all of the old thread locker compound is washed away.


The Locktite Primer 7471 is an acetone/alcohol based cleaner that helps prepare the surface materials for bonding. It will aid in mating the two dissimilar materials together and provide a stronger hold.



Application of Locktite Primer 7471




Application of Locktite Primer 7471

Edited by StrangerDanger
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Application of Locktite Primer 7471

9. Timing The Receiver Extension

The Receiver Extension must be timed in order to correctly use the collapsible stock. If you have the collapsible stock, install the tail portion of the stock at this time and collapse it fully. Use the comb of the stock as an index point to align the Receiver Extension. The comb of the stock should point dead center to the rear iron sight housing. Once aligned, remove the stock.


Thread the lock-nut over the Receiver Extension and tighten it. I highly recommend applying Locktite Primer 7471 and Red Locktite 271 to lock-nut too. Re-check your alignment with the stock to make certain it is straight. Apply about as much torque to the lock-nut as it took to break the lock-nut free during disassembly. You do not want to risk twisting your Receiver. Be generous with the Red Locktite 271 on this install. You do not want your Receiver Extension coming loose during recoil. I applied Red Locktite 271 to the backside of the lock-nut where it seats against the Receiver.


Application of Red Locktite 271

Edited by StrangerDanger
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This is the best method for setting the timing of the Receiver Extension. Make sure the stock is fully closed and locked in position when taking your measurements. You'll notice that the Receiver Extension can be turned by hand easily. So once you've determined where you want it, be very careful during your removal of the stock so that you do not disturb the Receiver Extension's position.



You can use a silver Sharpie or a pencil to add witness lines on the Receiver and the Receiver Extension if you feel necessary.

Edited by StrangerDanger
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After you've torqued the lock-nut down, the Red Locktite 271 will obviously be all over the place from displacement. Wipe up the excess. I found Q-Tips with Mineral Spirits did an excellent job at removing the excess.


10. Re-install the receiver extension internals

Lubricate the bearing surfaces of the Recoil Spring Plunger and insert it into the bottom of the Receiver Extension. Insert the Recoil Spring over the bottom of the Recoil Spring Plunger and push the Recoil Spring Plunger all the way in. Compress the Recoil Spring and insert a punch through the drainage hole to help retain the Recoil Spring. 



Edited by StrangerDanger
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The best way I found to compress the Recoil Spring is to hold the Receiver Extension in your right hand so your thumb and pointer finger are over the bottom opening and grasping the Recoil Spring. With your left hand, grasp the Recoil Spring approximately three inches below the Receiver Extension. Compress the three inches into the receiver extension. With your right hand, grasp the newly compressed portion of Recoil Spring. Continue to do this until most of the Recoil Spring has been pressed into the Receiver Extension. Insert a punch through the upper drainage hole to retain the Recoil Spring. This will allow you to use both hands to compress the remaining amount of Recoil Spring and begin threading the Stock Retaining Screw into the Receiver Extension.


Use the Magna Bit driver to tighten the Stock Retaining Screw until it bottoms out inside the Receiver Extension. Then use the snap-ring pliers to install the Stock Retaining Ring.



You can screw in the Stock Retaining Screw by hand most of the way. I pressed my thumb against the part, and twisted my thumb to put it 90% of the way home.

Edited by StrangerDanger
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Here the Stock Retaining Ring is fully seated. I tap on the Stock Retaining Ring with a large flat punch and a small hammer to make sure it is seated fully.


12. Reassemble the weapon

Perform a function test of the weapon to ensure that it is functioning properly. Ensure that you properly lubricate the Receiver after degreasing the action. You'll notice a difference when you pull the bolt to the rear if you haven't re-lubricated the weapon. I would recommend testing the safety, trigger and disconnector.


That concludes the tutorial on how to disassemble and reassemble the Receiver Extension on the Benelli M4. Hopefully it was clear and will be of use to some users in the future. I will leave the photographs up as long as photobucket remains free.




The way the M4 was meant to be.

Edited by StrangerDanger
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