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How to make a folding stock for your Benelli M3

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After getting positive feedback for my Benelli M3 folding stock mod in the shotgun pictures thread I’ve written this guide in case anyone else wants to do the same. However, be warned that there is a slight problem with this build which I will detail at the relevant point in the guide, but to a certain extent it renders the guide incomplete unless I can get a certain part identified or anyone following this can think of a better solution than what I cobbled together.






Please note that I’m not a particularly techy guy, I’m not that familiar with using tools or fixings so apologies if I refer to things without their proper name, where needed I have looked up the names of some particularly vital parts (such as the size and designations of the bolts I used).


The mod is based on two key components:

- A standard Benelli M3 pistol grip (as found on the Marui shorty and DE clones)

- An ATI synthetic top-folding stock, specifically this model: ATI Folding Stock


Note: Both these items are going to get chopped around a bit, if you have any reservations about doing this then don’t attempt the mod. I sourced a separate M3 pistol grip to do this and still have my original grip which came with the gun. I would recommend anyone else attempting this mod do the same.


You will need:

- A Hacksaw

- A Junior Hacksaw

- A vice/clamp (something to hold stuff in securely while you butcher it)

- A selection of hand-files

- Sandpaper of varying grits depending on desired finish

- A Dremel (optional) - If you wish you can use a Dremel in place of or in tandem with the hand files, I started off using a Dremel but ultimately switched to the hand files as I found them more useful for this work.


- A drill – you’ll need a Bit that will allow 5mm diameter bolts to pass through the holes you drill with relative ease, I had access to a selection and just judged this by eye. I used a hand drill but an electric one would be fine.


-Various bolts, washers and other bits detailed later at their relevant points



Stage 1.



You’ll need to disassemble the ATI stock so that you have the stock ‘arm’ separate from the pistol grip. You don’t need the grip supplied with the kit but many of the other parts are used in this mod, put them on one side for now.


I couldn't find a picture online of all the parts but the main components you'll need from it are these:


a thick round disc with a domed surface



a short length of plastic rod with another similar disc on one end of it



Plus the stock arm itself of course.


The M3 pistol grip also needs some disassembly, assuming yours comes with the bolt and sling loop attached you need to remove these and set them aside. The M3 manual which comes with the TM shotguns (I am unsure about the DE clones) and is hosted on Arnie’s will show you how to do this (it involves a pair of needle-nose pliers and a small screwdriver, it’s fiddly as hell but persevere and you’ll manage it).


Stage 2.



The majority of the work to be done is on the M3 pistol grip, to start with you need to remove a section of the grip assembly, see pics below.


Default Grip:



Where you need to cut:



You need to make a straight cut through the solid red line in the picture, avoid doing this from the top of the grip as you can’t see if the cut is straight from there. The dotted red line should not be cut, it simply shows the angle at which the cut needs to run. I used a hacksaw and approached it from the side and underneath. You essentially want to cut perpendicular to what you will see is effectively a large and flat square surface behind the shaped parts which stick out (ie: the bits you’re cutting off). If you stick to the line you shouldn’t have any problems, also take great care not to cut off the part highlighted in green in the above image. Once done tidy up the edge of where you have cut with files/sandpaper/Dremel, you should get something like this:



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Stage 3.



Once you’ve done this you will need to grind down the material on the sides of the grip, highlighted in red in the picture below.




As I mentioned above, I started off using a Dremel but in the end concluded hand files and sandpaper did a better job. What you’re doing here is providing clearance for the arms of the ATI folding stock to allow it to close properly and sit flush to the top of the receiver. Remove some material and then trial-fit the folding stock arm to the lugs on the M3 pistol grip. Note that you will likely have to wrestle the stock arm a bit to get it onto the lugs of the M3 grip but it should fit with a bit of effort and some cursing.

With the stock on attempt to fold it up so it sits completely flush to the top of the grip, if you’ve removed enough material from the side protrusions this will work, if not it will resist being closed and sit at an angle, if this is the case remove the stock arm and file/Dremel away more material until this works. When you’ve taken off enough material smooth out and finish the area with files and varying grits of sandpaper.


Stage 4.



Now go back to your remaining ATI parts, you should have a thick round disc with a domed surface and then a short length of plastic rod with another similar disc on one end of it.








Using the Junior hacksaw and a vice/clamp remove the rod from the disc, try to do this as cleanly as possible cutting perpendicular to the surface of the disc. We want to salvage the disc not the rod here, you’ll likely have to file/sand the disc once you’ve finished cutting to clean up any rough surface left by the saw.

Put the disc you just cut from the rod in a clamp or vice and drill through the existing hexagonal hole to allow a 5mm diameter round bolt. The other disc doesn’t need any modification.

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Stage 5.



If it isn’t already attached put the stock arm onto the M3 grip so it sits on the lugs.


You will now need some specific items:




Two small (minimum of) 5mm (inner diameter) washers (green box in pic above)

One large 5mm (inner diameter) washer (red box in pic above)

One M5x90mm bolt and nut* (below)

M3 Grip sling loop (optional)




*First of all, I used a 90mm bolt because I wanted to accommodate the M3 sling loop, in using this length I still need to cut off a short section from the end as it sticks out too far past the nut. You may well be able to use a shorter bolt if you aren’t bothered about the sling loop, I would suggest between 80-85mm but I am not certain about this. The bolts are designated M5 as this is both the diameter of the bolt (5mm) and the thread type. Coincidentally it appears the thread for the bolt which attaches the grip to the Marui receiver is also M5. You can buy M5 bolts of varying lengths online or in hardware stores, I got some 90mm M5’s with allen heads from an ebay store which sells parts for bikes.


Now, take your M5 bolt, if you’re using the sling loop put this on the bolt now. Put one of the small washers onto the bolt, followed by the unmodified domed disc. After that put on the large washer then put the bolt through the hole in the centre of the left-hand lug and out the other side, push the domed disc so it seats itself into the depression on the folding stock arm. Now put the other domed disc onto the protruding bolt on the right hand side of the grip, followed by the second small washer and lastly the nut. Tighten it up (not too tight).


Stage 6.



At this point I should mention a few things.


The M3 grip I used was, in fact, broken when I got it (I knew this before I bought it) so that it could no longer be attached to the receiver via the original bolt; a piece of plastic had come away from the inside where it meets the receiver and where the head of the bolt sits to hold the grip assembly to the receiver. Essentially if you put the grip on, put in the bolt and tightened it up the grip assembly would slide straight off the back of the gun - useless. I was originally using this grip for a ‘trial run’. However, I found that by using an M5x90mm bolt with a thick rubber washer (5mm inner diameter) on the outside surface of the grip I could successfully attach this grip to the gun. Now chances are you have an unbroken M3 grip and won’t need to go to such lengths but it lead to another part of the build being successful in a roundabout way. Allow me to explain:


At this stage I had a modified grip attached to the shotgun with a floppy stock arm hanging off it and no clue how to stop the arm from flopping.


Cue weird mystery plastic part:












I have no idea what this thing is, I found it in my Dad’s garage in his ‘fixings’ tray (he doesn’t know what it is either). As far as I know there was only one of them in there. I picked it up by chance thinking it might be useful to the build but I didn’t realise how crucial it would be until I started messing around in desperation.


I found that by using this part for the bolt to go through in place of the ‘thick rubber washer’ and then setting it at a 90 degree angle with the nub protruding to the left it would hold the stock arm in place in the unfolded position.


If anyone can ID this thing it would be very helpful as I can then edit this guide to help anyone looking to do this mod. The tricky thing is it could be anything from a plumbing bracket to the foot of a washing machine. Otherwise I’m afraid you’re going to have to come up with something else very clever to stop your stock from sagging when unfolded.


So there you have it, my incomplete guide to adding a folding stock to a Benelli M3. On the one hand I have the overwhelming sense of achievement at having made this work for me, but on the other is the disappointment in not being able to figure out a method of retaining the stock in the unfolded position which can be easily reproduced for others to follow. I hope someone can ID the mystery part so this guide is actually useful.


edit: for what its worth I think this mod would have been easier with a G&P metal 870 folding stock but I was unable to source one for this build.

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