angryeyebrows
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- Oscar Mike
The same procedure can be applied to any shotgun stock but I used a Benelli M4 pistol grip stock for my project. I've also posted the article on my website here:
http://tyrdynamics.com/benelli-m4-stock-reduction.html
Intro
A common problem with the Benelli M4 Super 90 is that the factory stocks are too long for use with body armor or bulky clothing. The factory collapsible stock does have a usable middle position, but due to its design it prohibits the use of the ghost ring sights and when fully extended it is the same length as the fixed stocks. The only other stock on the market that offers a reduced length of pull for the Benelli M4 is the Mesa Tactical Urbino stock and until Mesa fixes the issues I have noted in my review, that stock is not an option.
I decided to do what others have done and chop down a factory pistol grip stock. My goal was to reduce the stock from the 14” factory length of pull to approximately 12”. I also was not a fan of the attachment method of the factory M4 stock so I decided to redesign it. Here is what I used for supplies:
Chop Mod
The first thing I did was remove the recoil pad from the factory stock using the Philips screw driver. This can be discarded as it will no longer be used. I then measured from the back of the stock using my ruler and marked off with the pencil the amount I wanted to remove. After that I took the PVC saw to the stock, being careful that I kept the line straight and stayed just on the outside of my pencil line. Using the sandpaper I touched up the edges and checked the stock with the level. Once I was happy that everything was flat, it was time to fill in the back with the Marine-Tex, in order to provide new anchor points for the recoil pad.
Using the Dremel with the sanding wheel, I roughed up the inside top and bottom of the stock to aid in the gripping strength of the epoxy. The Marine-Tex worked quite well although it was a little difficult to manipulate it into the correct spots on the stock. I ended up simply slopping it in with a small putty knife and then covering the back of the stock with plastic wrap so I could stand the stock on end to let it set. After the Marine-Tex is fully hardened, you can begin cutting and sanding using the Dremel in order to clean up and smooth out your work.
The next step was to fit the recoil pad and prepare it for grinding. The best way to do this is to align the pad with the back of the stock, and using the centre punch lightly mark the positions for the new screw holes through the back of the pad. Then, using the 1/8th drill bit, drill a pilot hole for the screws. Mount the pad using the Philips screwdriver. Ensure that you use Vaseline to lubricate the screw holes of the pad so they don’t tear. Once the pad is mounted, trace around the back of the pad, using the outside of the stock as a guide, so you can clearly see what material will need to be removed. Using the belt sander, you need to carefully grind down the pad. The LimbSaver comes with directions for the best way to do this. To finish the process, you can use the 220 or finer grit sandpaper to smooth out and fine tune the edges of the pad.
Showing How Much Material Was Removed (2 1/4")
Back Filled with Marine-Tex, Cut Out and Sanded Down
Installing the Newly Ground Down Pad
Redesign
The next thing I didn’t like about the stock was the method used to mount it to the shotgun. The factory stock has a fixed bolt in the back that is not meant to be removed. This bolt holds the stock to the gun as well as retains the sling plate. To install the stock, the trigger group is removed and the stock is spun onto the back of the recoil spring tube. Then the trigger group is replaced and prevents the stock from spinning off. The problem with this is that you can never get the stock as tight as you need it and a good sharp smack of the grip will cause the stock to cant, despite the trigger group blocking it from rotating.
My idea was to replace the factory mounting assembly with a much simpler design using a socket cap screw and a washer. I realize the factory stock was designed with tool-less disassembly in mind, but being able to remove the stock without tools is not something I really need. I also wanted to do something to further prevent the accidental canting of the stock. So I decided to make use of the small blind hole in the back of the M4’s receiver located just above the recoil spring tube. This is where the stainless steel dowel pin comes in. I carefully measured the distanced and used the punch to mark the stock. Then using the drill, I drilled out a hole that was approximately 5/16th deep. I then used the J-B Kwik to permanently install the pin into the front of the stock.
Anti-Rotation Pin Installed
Removal of the Factory Nut
Using the Coupling Nut to Drive Out the Factory Bolt
Removing the mounting hardware was a bit more of a task. It consists of a long specialized bolt, a bunch of spacer washers, an anti rotation plate and a lock nut. Because it was not designed to be user removed, the bolt is installed at the factory with some sort of thread locker. The first step is to remove the lock nut from the back. It was very tight. Once the nut was off the next step was to use the coupling nut to join the cap screw and the rear of the bolt. This allows you to tighten the cap screw until it bottoms out on the bolt which will force the bolt to screw all the way through the anti rotation plate as you keep tightening. The plate may need to be heated to loosen the thread locker. I simply used brute strength and my socket wrench and eventually it broke free. I was able to finish the rest by hand. Once the bolt is out, the entire assembly falls out into pieces. I reinstall using my new socket cap screw and one of the spacer washers from the original assembly.
Factory Parts Removed
Replacement Parts
New Parts Installed
Finished Project
Conclusion
The stock is much more comfortable to use now and is the perfect length. With the addition of the recoil pad, the true length of pull is slightly less than 12.5”. I think the whole thing turned out great and now all that is left for this project is to replace the factory sling plate with a Noveske QD plate. It takes a bit of time an effort, but in the end I believe this is the best option for a stock on the market today.
http://tyrdynamics.com/benelli-m4-stock-reduction.html
Intro
A common problem with the Benelli M4 Super 90 is that the factory stocks are too long for use with body armor or bulky clothing. The factory collapsible stock does have a usable middle position, but due to its design it prohibits the use of the ghost ring sights and when fully extended it is the same length as the fixed stocks. The only other stock on the market that offers a reduced length of pull for the Benelli M4 is the Mesa Tactical Urbino stock and until Mesa fixes the issues I have noted in my review, that stock is not an option.
I decided to do what others have done and chop down a factory pistol grip stock. My goal was to reduce the stock from the 14” factory length of pull to approximately 12”. I also was not a fan of the attachment method of the factory M4 stock so I decided to redesign it. Here is what I used for supplies:
- PVC Saw
- Drill (1/8th and 5/32nd Drill Bits)
- 100 grit and 220 grit Sandpaper
- J-B Kwik
- Marine-Tex Epoxy (2 oz. Grey)
- M8-1.0 Coupling Nut (Made with a M8-1.0 Tap)
- M8-1.0 Cap Screw (60mm)
- M8-1.0 Socket Cap Screw (60mm, Oxide)
- 5/32nd 0.5” Stainless Steel Dowel Pin
- LimbSaver Low Profile Grind to Fit Recoil Pad
- Belt Sander
- Philips Screw Driver
- Large 6mm Allen Key
- 13mm Deep Socket, Extender and Wrench
- Vaseline
- Mechanical Pencil
- Ruler
- Level
- Dremel (Cutting Wheel and Sanding Wheel)
- Centre Punch
Chop Mod
The first thing I did was remove the recoil pad from the factory stock using the Philips screw driver. This can be discarded as it will no longer be used. I then measured from the back of the stock using my ruler and marked off with the pencil the amount I wanted to remove. After that I took the PVC saw to the stock, being careful that I kept the line straight and stayed just on the outside of my pencil line. Using the sandpaper I touched up the edges and checked the stock with the level. Once I was happy that everything was flat, it was time to fill in the back with the Marine-Tex, in order to provide new anchor points for the recoil pad.
Using the Dremel with the sanding wheel, I roughed up the inside top and bottom of the stock to aid in the gripping strength of the epoxy. The Marine-Tex worked quite well although it was a little difficult to manipulate it into the correct spots on the stock. I ended up simply slopping it in with a small putty knife and then covering the back of the stock with plastic wrap so I could stand the stock on end to let it set. After the Marine-Tex is fully hardened, you can begin cutting and sanding using the Dremel in order to clean up and smooth out your work.
The next step was to fit the recoil pad and prepare it for grinding. The best way to do this is to align the pad with the back of the stock, and using the centre punch lightly mark the positions for the new screw holes through the back of the pad. Then, using the 1/8th drill bit, drill a pilot hole for the screws. Mount the pad using the Philips screwdriver. Ensure that you use Vaseline to lubricate the screw holes of the pad so they don’t tear. Once the pad is mounted, trace around the back of the pad, using the outside of the stock as a guide, so you can clearly see what material will need to be removed. Using the belt sander, you need to carefully grind down the pad. The LimbSaver comes with directions for the best way to do this. To finish the process, you can use the 220 or finer grit sandpaper to smooth out and fine tune the edges of the pad.
Showing How Much Material Was Removed (2 1/4")
Back Filled with Marine-Tex, Cut Out and Sanded Down
Installing the Newly Ground Down Pad
Redesign
The next thing I didn’t like about the stock was the method used to mount it to the shotgun. The factory stock has a fixed bolt in the back that is not meant to be removed. This bolt holds the stock to the gun as well as retains the sling plate. To install the stock, the trigger group is removed and the stock is spun onto the back of the recoil spring tube. Then the trigger group is replaced and prevents the stock from spinning off. The problem with this is that you can never get the stock as tight as you need it and a good sharp smack of the grip will cause the stock to cant, despite the trigger group blocking it from rotating.
My idea was to replace the factory mounting assembly with a much simpler design using a socket cap screw and a washer. I realize the factory stock was designed with tool-less disassembly in mind, but being able to remove the stock without tools is not something I really need. I also wanted to do something to further prevent the accidental canting of the stock. So I decided to make use of the small blind hole in the back of the M4’s receiver located just above the recoil spring tube. This is where the stainless steel dowel pin comes in. I carefully measured the distanced and used the punch to mark the stock. Then using the drill, I drilled out a hole that was approximately 5/16th deep. I then used the J-B Kwik to permanently install the pin into the front of the stock.
Anti-Rotation Pin Installed
Removal of the Factory Nut
Using the Coupling Nut to Drive Out the Factory Bolt
Removing the mounting hardware was a bit more of a task. It consists of a long specialized bolt, a bunch of spacer washers, an anti rotation plate and a lock nut. Because it was not designed to be user removed, the bolt is installed at the factory with some sort of thread locker. The first step is to remove the lock nut from the back. It was very tight. Once the nut was off the next step was to use the coupling nut to join the cap screw and the rear of the bolt. This allows you to tighten the cap screw until it bottoms out on the bolt which will force the bolt to screw all the way through the anti rotation plate as you keep tightening. The plate may need to be heated to loosen the thread locker. I simply used brute strength and my socket wrench and eventually it broke free. I was able to finish the rest by hand. Once the bolt is out, the entire assembly falls out into pieces. I reinstall using my new socket cap screw and one of the spacer washers from the original assembly.
Factory Parts Removed
Replacement Parts
New Parts Installed
Finished Project
Conclusion
The stock is much more comfortable to use now and is the perfect length. With the addition of the recoil pad, the true length of pull is slightly less than 12.5”. I think the whole thing turned out great and now all that is left for this project is to replace the factory sling plate with a Noveske QD plate. It takes a bit of time an effort, but in the end I believe this is the best option for a stock on the market today.
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