Benelli M4 -- Shell Stop Removal & Install

[StrangerDanger]

Hi all,

I had a request to do a detailed pictorial on the disassembly of the Shell Stop. Removal of the Shell Stop is the same for the factory and GG&G model. In fact, the GG&G model is simply a modified factory Shell Stop.

 

Start out by unloading the weapon and setting the ammuntion away from the work area. Field strip the M4, remove the barrel assembly, bolt carrier and trigger group. The stock may be left on.

 

 

This is a view of the inside of the receiver. It shows the placement of the Shell Stop Spring. The spring is a loose fit, so you should note its position before disassembly.

[StrangerDanger]

In this photograph, the Shell Stop Pin is annotated over the photograph. This is the only pin that retains the Shell Stop and Shell Stop Spring in place.

 

In this photograph, the red line indicates the Shell Stop Pin channel. The Shell Stop Pin passes through the guide rails that the bolt carrier rides along.

[StrangerDanger]

This is the top of the Shell Stop Pin channel.

 

The blue lines indicate the channel that the bolt carrier reciprocates in. The red line shows the placement of the Shell Stop Pin.

[StrangerDanger]

I find it best to use a punch to drive the Shell Stop Pin out from the bottom upward. I don't usually remove the pin completely from the receiver. I drift it upwards enough to remove the Shell Stop.

 

Once the pin has been drifted into the channel that the bolt carrier reciprocates in, the punch will act as a slave pin holding the Shell Stop into the receiver.

[StrangerDanger]

This angle shows the Shell Stop Pin protruding through the rail and part of the way out of the ejection port. As the punch is removed from the receiver, the Shell Stop and Shell Stop Spring will fall out of the receiver.

 

[StrangerDanger]

The Shell Stop Spring simply sits in the recessed groove at the rear of the Shell Stop.

 

This is the back side of the Shell Stop. The edge at the left is what retains the shells within the magazine tube. The right side indexes with the Shell Drop Lever in the trigger group.

[StrangerDanger]

This photo shows the base of the Shell Stop Pin drifted up high enough for the Shell Release to be removed from the receiver. The pin is visible protruding through the ejection port.

 

 

[StrangerDanger]

This image shows the Shell Stop and how it indexes with the Shell Release Lever.

 

Now it is time to reinstall the Shell Stop. Insert the Shell Stop Spring into the Shell Stop.

[StrangerDanger]

 

Place the Shell Stop and Spring back into the receiver. Try to keep the spring properly aligned at the rear of the Shell Stop.

 

 

 

Compress the Shell Stop and insert a slave pin through the Shell Stop Pin channel until it makes contact with the Shell Stop Pin. It'll take some effort to align the Shell Stop. I typically look down the hole of the Shell Stop Pin channel and visually align the holes. Then insert the slave pin to keep the assembly together.

[StrangerDanger]

 

This image shows the slave pin in place. I applied blue painters tape to the top of the ejection port to protect the finish.

 

 

Here, I am using a roll pin holder that slips over the end of the Shell Stop Pin. I drove the pin back down and displaced the slave pin.

[StrangerDanger]

 

This image has the bolt carrier channel superimposed over the receiver to show you the exact depth needed to seat the Shell Stop Pin. While driving the pin in, I squeeze the Shell Stop against the Receiver. This aids in aligning the holes for the pin to transit. When you're tapping the pin in, you have to listen and feel for the pin actually drifting. If it sounds like you're delivering a dead blow to the pin and it isn't moving, stop and back the pin out from the opposite way if needed. You don't need a lot of force to move this pin. I use a 4 ounce hammer with maybe a 4 inch swing.

 

 

At this point, the roll pin holder has bottomed out against the ejection port. Now I'll switch to a roll pin starter punch.

[StrangerDanger]

 

The dimple on the end of the Roll Pin Starter Punch indexes with the hole in the Roll Pin. These keep the punch from slipping off the roll pin.

 

 

This is the best way to hold the tool and still apply pressure to the bottom of the Shell Stop. The blue line shows the current position of the Shell Stop Pin. It's still obstructing the channel for the Bolt Carrier at this point.

[StrangerDanger]

 

In this shot, it shows that the roll pin has not been seated far enough down the channel. A portion of the pin is protruding into the channel for the Bolt Carrier.

 

 

In this image, the roll pin has been seated successfully far enough into the channel. Be sure that you do not seat it too far though. The roll pin should not protrude from the bottom of the receiver at all either.

[StrangerDanger]

 

Here is why taping up the receiver is a good ideal.

 

 

If you're installing the GG&G unit, note how the pad indexes with the keyed Shell Stop button. I noticed that the button will fit differently if you rotate it 180 degrees. In one position, the button rides higher up the receiver. Neither is wrong, it is just personal preference.

[StrangerDanger]

Here the Shell Stop Release pad is dry fit to the button face.

 

A small amount of thread locker is recommended for the bolt pad face.

[StrangerDanger]

At this point, the assembly is complete. Function test the weapon and the bolt release to ensure that it is performing correctly.

 

 

[Amsdorf]

Thanks, great job.

[Hookster]

Wow SD!!! Thanks for all your good efforts on this one... I was actually planning to install my GG&G pad this weekend so your timing with this thread is excellent. I think I'll pick up the roll pin holder and starter punch. I just have a regular punch set and I always get a little nervous dealing with roll pins. Nothing like the right tools for the job to make sure all goes well.

 

 

Thanks and Take Care,

 

 

Hookster

[FLAWLS1]

Cool, awesome thread with the pictorials. It'll help everyone out whoever does this.

[StrangerDanger]

Another user sent me a tip about putting a self adhesive velcro sticker on the back side of the pad if you want to prevent it from marring your receiver. My receiver is already pretty well beat up, so it didn't matter to me if it scratch the finish.

 

In a month or two, I'm going to do a pictorial on how to tear down the receiver extension when I get my extra extension back from WMD Guns.

[StrangerDanger]

Brownells Roll Pin Holders Punches

http://www.brownells.com/.aspx/pid=781/Product/ROLL-PIN-HOLDERS

 

Brownells Roll Pin Starter Punches

http://www.brownells.com/.aspx/pid=20640/Product/ROLL-PIN-STARTER-PUNCHES

[StrangerDanger]

Brownells Roll Pin Punch Set & Bench Block

http://www.brownells.com/.aspx/pid=27552/Product/ROLL-PIN-PUNCH-SET

 

Brownells Alignment Pins

http://www.brownells.com/.aspx/pid=364/Product/ALIGNMENT-PUSH-PUNCHES

I only have the steel set of these. I really didn't have much purpose for the brass ones. However, sometimes it would be nice to have two of the same size alignment pins.

[StrangerDanger]

Brownells Dental Picks

http://www.brownells.com/.aspx/pid=9809/sku=700-410-000/Product/Dental-Explorers-Set

http://www.brownells.com/.aspx/pid=25538/Product/STAINLESS-STEEL-DENTAL-SCALERS

Buy these. I used to bend paperclips to try to capture spring legs. Do yourself a favor and buy these and save yourself the headaches involved. Note there are different styles available. I tend to use the scalers the most due to the tip strength.

[StrangerDanger]

Brownells Dental Picks continued.

http://www.brownells.com/.aspx/pid=25539/Product/STAINLESS-STEEL-S-4-SCALER

[ErnieB73]

I know this thread is ancient but anyone know the actual size punch that is needed for this?