I must admit, I love the Benelli Super 90 series. Not only are the Tacti-cool but they are monotonously reliable. That being said, I hate the length of pull of the factory stocks. I swear that the LOP was designed for chimpanzees. Though I am a novice, I would not let that deny me. My shortened stock was originally from a Benelli M3 that has since been sold. The buyer wanted a factory stock so I was forced to buy another factory atock and I kept the modified short stock.

When I originally posted my chopped stock, no one paid notice.


It wasn’t until recently, when I posted pictures of my stock with my 14” entry gun that I received a few inquiries.



I decided to post some pictures and plans of my conversion.  



Things you will need:

5/32 Drill bit
Drill
Marine Tex (color doesn’t matter)
Masking tape (blue and Beige)
Belt Sander
Dremel
Cutoff wheel
Grinding wheel
Saran Wrap
Sanding block
60 Grit Sandpaper
100 Grit Sandpaper (or finer)
Limb Saver Grind to fit recoil pad (make sure to get the small size)



1. Determine your desired length of pull. I used An AR-15 lower with collapsible stock to determine my desired LOP. You can use blue masking tape to demarcate this line. Go ahead and be generous in the application of this masking tape. You will need some extra layers to protect the stock when you fit the recoil pad.


2. Apply another layer of beige masking tape approx. ¼ - ½ behind the desired length of pull. Use the beige masking tape as a cutting guide. Make sure you leave enough material between the initial cut and the desired length of pull. This is important as you will use the belt sander to smooth the uneven cut you will make in step 3.    
 
3. I used a cutoff wheel on my Dremel to make the initial cut on the stock. Any cutting tool will work; i.e. band saw, table saw, hack saw etc. etc. Heck, feel free to use any other cutting tool that you want to remove the bulk of the material. We will use the belt sander to grind down and get reasonably close to the desired length of pull.


4. Using your belt sander, grind down the uneven cut made in Step 3. Keep in mind the angle of your cut and try to keep the drop as close to factory as you can. I used the factory recoil pad as a guide to keep the drop angle as close to factory as possible. As you get close to the blue layer of masking tape, be patient! Check your work constantly by placing the stock on a level surface and verify that you are grinding the stock down evenly. Any cheap bubble level should work. NOTE:  The bubble level should be even when it is running port and starboard. Not north and south. See illustration

5. Once you verify that your desired length of pull is even and duplicates the factory drop, we are ready to apply the Marine-Tex. Use your trusty Dremel and a grinding wheel to roughen the upper and lower portions of the surface of the interior of the stock. This gives the Marine-Tex extra holding power.

6. Mix enough Marine-Tex to fill both the lower and upper portions of the interior of the factory stock. Marine-Tex is pretty thick and maintains a paste like consistency. Keep in mind the middle must remain open to facilitate the removal and attachment of the stock.

7. Use the Saran Wrap between the small grind to fit recoil pad and the factory stock. Stand the stock up on the recoil pad so that the Marine-Tex will fill in flatly. A hair dryer helps speed up the curing process. The end result will look like this, (just not as smooth):

8. Once the Marine-Tex is dried, verify that the stock is still even. Refer to the illustration is Step 4. If it is not even, use your sanding block with 60 grit sandpaper to flatten the rear portion of the stock. Finish with 100 or 150 grit sandpaper to get it smooth. Once it is completely flat and level you are ready for the next step.

9. Place the grind to fit recoil pad on the stock. Use a punch or screwdriver to demarcate the holes for the stock screws.

10. Find the two markings for the stock screws in the Marine-Tex. Using a 5/32 drill bit, drill through these two markings in the Marine-Tex. Try to keep your drill as straight as possible.

11. Place a screw into one of the holes. Use your drill to drive the screw through the hole. The screw will self tap making removal a snap. Repeat for the other hole.
12. Now attach the grind to fit recoil to the stock using the factory screws.
13. If your layer of blue masking tape is gone now is the time to add a couple more layers.

14. Use your belt sander to grind down the recoil pad. The blue masking tape will keep the belt sander from biting into the stock while you grind down the pad.
15. Once the desired profile is reached, remove all blue masking tape and the recoil pad.
16. Put the stock back on your gun and enjoy!



I am just a hobbyist so please proceed at your own risk. I am sure these methods can be used for any polymer shotun stock.

I might have to try this.  Thanks for the writeup.

Looks really good.  I've used a similar method to shorten synthetic stocks for a while using fiber-reinforced Bondo.  Is the Marine Tex about the same material?  How long does it take to set up?

If you want to change the angle of the stock use a piece of poster board and draw an outline of the present stock on it making sure to get a good trace all the way around.  Use a sliding "T" bevel to adjust the angle on your drawing and then lock it.  Slide it toward the receiver end of the drawing the amount you want to shorten the stock, making sure to keep the edges even on the base of the bevel and the drawing, and mark your new cut off line.  Extend the angled "cut" marks 2" beyond the outline of the stock so you can lay the stock on the outline and get a visual on it before you cut.

Use the locked bevel to mark your cut line on the taped stock and the cardboard diagram to check that your staying in the dimensions you want.

Rob

edited to say:  Your pics are great! Wish I could do as good on those.

Quoted: I might have to try this.  Thanks for the writeup.

Thanks!

Quoted: Looks really good.  I've used a similar method to shorten synthetic stocks for a while using fiber-reinforced Bondo.  Is the Marine Tex about the same material?  How long does it take to set up?

Marine-Tex is often used as a bedding compound for wood stocks. It is a two part epoxy that is used on boats as well as in the gun industry. I have never used Bondo but I believe that it is probably similar. Marine-Tex typically takes a couple hours to set up. I always use my wife's hair dryer to speed it up though. The best price that I have found is Brownells through their wholesale account. It is very easy for anyone to set up a wholesale account.

Quoted: If you want to change the angle of the stock use a piece of poster board and draw an outline of the present stock on it making sure to get a good trace all the way around.  Use a sliding "T" bevel to adjust the angle on your drawing and then lock it.  Slide it toward the receiver end of the drawing the amount you want to shorten the stock, making sure to keep the edges even on the base of the bevel and the drawing, and mark your new cut off line.  Extend the angled "cut" marks 2" beyond the outline of the stock so you can lay the stock on the outline and get a visual on it before you cut. Use the locked bevel to mark your cut line on the taped stock and the cardboard diagram to check that your staying in the dimensions you want. Rob edited to say:  Your pics are great! Wish I could do as good on those.

Excellent advice! By laying it out on cardboard you have a great visual on the desired angle. Your way sounds better than my way as I was just eyeballing it. A person could use your way and then refer to step 4 of my process to make sure it is even.

I used to cut stocks on a homemade jig I threw together with adjusting screws to square and level the stock using a mitre saw to make the cut.  Some years ago I purchased a saw called a buck saw and found out it works great for cutting gunstocks, both wood and synthetic.

A buck saw, at least that's what I was told they're called, is a compound mitre saw with a radial arm feature, mine's got a 7.5" blade and a 10' horizontal movement.  I use a plywood blade, can't remember the TPI count but it's a lot.  Using the factory cut butt end of the stock to square and level the stock and the locking screw pad on the saw to hold it in place I've yet to make a cut that wasn't perfect the first time.  (on a good stock that is, I had a few old take-offs laying around that I "cheated" on for practice)  Use playing cards under the pistol grip area (learned that from a Brownell's Gunsmithing Kinks book), and between the top of the stock and the back plate on the saw to adjust for perfect level and square.

I've found that if I come down on the top of the stock to make the initial half cut and then pull the saw back and use the radial arm feature to finish the cut there is very little to no chipping on either material.  I think the reason for this is the saw teeth are impacting the outer surface of the stock first, rather than "pressing" out from the inside on the bottom half of the stock.  The bottom outside is where I always had wood stocks chip even when well taped.

I'm not saying go out and buy one of these saws just for cutting stocks, but everyone probably has a buddy that's got one.



Rob

My gunsmith just did your mod to my 14inch M1S90.

Now I can handle it the way it should be handled!!

I printed it out , and handed it to him , went to the Riviera Maya for a week , came back and it was done.

Many thanks to you!!

Went shooting today and the stock performed perfectly. I really like the performance of the Limbsaver recoil pad.

Quoted: Nice how-to! Ever tried a Pachmayr Sporting Clays pad?  They're my favorite with that hard rubber heel insert which slides up your shirt better.

I have not tried the Pachmayr. The Limbsaver factory replacement pads are awesome. The grind to fit pads are a little stiffer but still perform way above and beyond the factory pad IMHO.

Can we get this tacked?  This is really good information.

Thank you
R/
Mike

What the crap!  Where were you last year.......wish that I had thought of this earlier.  Don't know why I didn't think about using Marine Tex or something similar INSIDE the stock. I bet that every rifle that I own is epoxy bedded in some way.  It never occurred to me that I could use it on my Mossberg.  I will give this a try, especially since I just bought myself a compound miter saw from Sears.

Thanks for the good write up.

Thank you for a Good Post w-Pics regarding a sm problem. CW