A while back I picked up a handful of surplus Vietnam-era synthetic stocks (1 nice one, 2 thrashed ones) with the idea of using them as a starting point, and after some experimentation, came up with a technique that I think is worth sharing. Depending on what materials are used, a nice stock can be built for as little as $150-$200. In this Instructable, I'll show a technique that I used to build 3 variations of a comfortable and functional stock.
What you will need:
- Donor stock - this can be a nice one, but it's better to use a structurally sound "less pretty" one as the nice synthetics are becoming harder to find - and the less "aesthetically pleasing" ones are a lot less expensive. Expect to pay around $20-30 for a solid candidate.
- A pistol-grip style buttstock. I've found the aftermarket stocks for the Mossberg 500 series shotgun seem to work well and have about the right shape as well as a good "keying" surface.
- Epoxy - I use a quality 30-minute epoxy. I find the faster-setting epoxies don't seem as strong and don't seem to bond as well - just my opinion, of course.
- A Tee-Nut that matches the buttstock mounting bolt you intend to use. 5/16" X18 X 7/8" in this case. I used the 3-hole version, not the barbed version of the tee-nut.
- Hot glue gun
- Fiberglass cloth or chopped fiberglass
- Petroleum Jelly to act as a parting compound or release agent
- A sculptable epoxy clay or similar (possibly fiber-filled bondo, but I like to use similar materials for better bonding)
- Paint - Duracoat in my case, but rattle-can paint would work, too.
- An electric handpiece, Foredom, or Dremel would be very helpful
- Various files, sandpaper (wet/dry aluminum oxide), clamps, hacksaw or sawzall, sander, etc
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Step 1: Design
When I originally decided to do this, I spent some time trying to find an aftermarket pistol-grip stock that seemed to have the same lines as the fiberglass stock. I took a picture of the fiberglass stock with the action in place against a light background, took the image into Photoshop and then ran the "Find Edges" filter. I did the same with a few product images that I found online of a few pistol-grip stocks. This gave me a line drawing of the shapes to work with and kept me from being distracted by shading. After trying a few different combinations, it seemed that the stocks designed for the Mossberg 500 shotgun were a good match, so I took the plunge and ordered an ATI adjustable stock.
One thing to keep in mind is whether you plan to use optics or not. In my case, I knew I wanted to use the iron sights, so I wanted a stock that would allow me to keep the same cheek-weld as the original stock. If you plan to use optics, you will either want a different shaped buttstock, or, one with an adjustable cheek riser (see the folding stock in this Instructable).
Step 2: Modifying the Stock - A.k.a. - the Point of No Return
Once you have the new buttstock in hand, it's time to figure out how to locate it and in turn, where to cut the stock. The easiest way for me is to just lay the new stock on the old one, make sure that the comb (cheek area) is lined up, and mark the angle and placement of the mating face. After this is done, I use a reciprocating saw with a bi-metal blade (you may hit one of the steel alignment pins in the stock) to cut shy of the line. Using a belt sander, I sneak up on the final line, stopping to check how the new buttstock will mate up as I go. Take your time - you can always take a little more off, but you can't put it back on. It might be helpful at this point to scoop out some of the foam that makes up the core of the stock so that you can fully fit the mating surfaces together to check trigger position relative to the grip and the buttstock's angle of attachment to make sure you like it.
Once you have it aligned and working, you can clean the foam out the cavity at the base of the stock. You'll want to remove as much foam as possible - and preferably grind all the way down to the fiberglass (but not through it, of course). I use a combination of carbide and tungsten burrs with an electric handpiece for this process and it goes very quickly. While doing this, try to break (round) any sharp edges - you want to avoid leaving any sharp corners inside the cavity as they tend to be what are known as "stress risers" and will often be the place that a crack will originate.
Step 3: Installing the Buttstock Anchor
I decided to use the 3-hole tee-nuts over the barbed versions because I wanted to control the shape of the cutouts and I was skeptical that the barbed versions would embed themselves as thoroughly - I thought the barbs might keep the epoxy/glass slush from fully flowing over the top of the flange and locking it in. I used a cutoff wheel in a 4" angle grinder to make the cuts - but anything that will cut metal will work. I also roughed up the entire outer surface of the tee-nut to give the epoxy more purchase.
I made the "chopped glass" by cutting up some fiberglass cloth to around 1/4" to 1/2" lengths and teasing the strands apart to make them more random.
The basic t-nut embedding process is this:
- Mount your tee-nut to the grip using the mounting bolt. Make sure that the tee-nut is short enough to allow the grip to fully seat against the front part of the stock - you do NOT want to find out it won't fit once the stock is packed with epoxy and glass.
- Figure out your clamping setup ahead of time - do a dry run to make sure everything will hold it's position while the glue cures. Leave your front stock clamped up in a vertical orientation. Check alignment twice.
- Take the bolt and tee-nut apart, coat the bolt with petroleum jelly and re-install the tee-nut. Make SURE you don't contaminate the outer surface of the tee-nut with petroleum jelly - if you do, clean it off thoroughly.
- Fill the end of the tee-nut with hot glue to keep epoxy from seeping into the threads.
- Mix about 2 tablespoons of epoxy (30-minute or longer setting is preferred)
- Mix glass strands into your epoxy. You're going for a paste-like consistency
- Pack the paste into the cavity. Do a decent amount of "packing" with a small stick or pointed instrument. What you are doing is trying to pack the material against the sides and force out any air bubbles.
- When you have the epoxy mixture packed in, press the stock with tee-nut into place. A slight side-to-side motion is helpful to kind of dig the tee-nut in and get material to squish up around the sides.
- Clamp your pistol-grip in place and wait for everything to cure. Even though the epoxy will seem cured in a couple of hours, don't put any serious torque on the tee-nut for at least 24 hours.
Step 4: Filling and "Keying" to Fit the Buttstock
Epoxy Sculpt is a two-part epoxy clay that once cured is *extremely* hard. It comes in three colors last time I checked - grey, black, and brown. If you want to buy it locally, check with a taxidermist supply - they tend to keep that kind of thing around ;) Epoxy Sculpt bonds to just about everything and is extremely hard to remove if it does bond to something you don't want it to (like a counter top) so keep that in mind. One interesting thing about it is that you can use water to smooth it and wash it off while it's still soft.
Some tips on mixing Epoxy Sculpt:
- Wearing gloves, pull out equal-sized portions of hardener and resin and roll them into balls.
- Mash the two balls together either between your hands or on a sheet of waxed paper.
- Tear the flattened layers in half and stack on top the other.
- Mash it all flat again, tear it, stack it, mash it, repeat.
- Once you get a lot of layers, go ahead and knead it all together. Doing it this way saves a lot of time and strain.
Once this is done, remove the spare bolt. Coat the mating bolt from the buttstock with petroleum jelly (be generous). Now, coat the Epoxy Sculpt AND the mating surfaces of the buttstock with petroleum jelly - you're trying to make sure you have a LOT of parting compound because like I said, Epoxy Sculpt will bond tenaciously with just about any surface - and if you want to be able to get your stock apart again to sand and paint it, well, the more parting compound the better :)
Using the bolt to draw the buttstock up tight, go ahead and smush (the technical term, of course) the buttstock into the clay. Snug up the bolt until you have a flush fit. Be sure to check that the pistol grip is centered and not canted to one side or the other, then go outside and play with the dog for a few hours while the Epoxy Sculpt sets up. You can speed up the cure by putting the stock in the oven at 150 degrees or so, but you didn't hear that from me - no fair blaming me when your wife catches you.
Step 5: Details, Finish Preparation, Finish
Once the Epoxy Sculpt has cured and you've managed to get the grip off the stock without breaking anything, go ahead and rough-shape the hardened clay with files or a Dremel. Rough up the slot in the right side of the stock that used to house the selector switch (if you want to plug that hole, anyway) and also, rough up the sides of the stock toward the rear - you're going to put another layer of Epoxy Sculpt on here to give you enough material to create a nice smooth transition from the pistol grip to the stock.
At this point, you're going to want to let your hands do the "seeing" to find any bulges or sharp corners that are uncomfortable or annoying - and get rid of them. Keep checking and adjusting the Epoxy Sculpt around the grip until it's smooth and comfortable to your hand. Don't worry about making this super - smooth - sanding to 150 grit should be enough - as long as you plan on using some filler primer in the next step.
Once the stock feels good, give it an overall roughing up with a scotchbrite pad and wash it thoroughly. I used a catalyzed urethane primer (filler primer) sold by Keystone. One thing great about this primer is that it wet-sands very nicely, and it's pretty hard - a great substrate for the Duracoat topcoat.
Final finish is Duracoat Matte Black and OD Green.
Step 6: Final Assembly
Just a few "beauty shots" of the stocks with action in place.
Thanks for reading - I hope you found something useful here!