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Gunsmithing Filling the butt end of a polymer stock?

SomeOtherGuy

Sergeant
Full Member
Minuteman
Feb 29, 2012
645
12
UP Michigan
I recently bought a Savage 10PC that comes with the accustock. This rifle is going to be used for ordinary hunting rifle purposes, not long distance precision, and I'm not looking to replace the factory stock with a $500 aftermarket stock. The aluminum bedding system seems to do a good job from the trigger forward to the forearm, which seems to be both straight and stiff. But from the trigger back it feels like a $5 toy stock from China. I would like to do something to make the butt end of the stock stiffer, heavier, and lose the hollow sound and feel. I was thinking of drilling a small hole in the shell and using spray foam (stuff you would use to insulate around windows and wall openings) to fill the hollow shell. Has anyone tried anything like this? Any other suggestions?
 
Re: Filling the butt end of a polymer stock?

You are probably on the right track if sound deadening is the major goal, but I would probably opt for a 2 part urethane foam instead of the stuff in the can. The canned stuff expands instantly when coming out of the tube and would probably be hard to get a complete fill. The two part foams pour in like a liquid and have varying expansion ratios depending on the density. I use the rigid foams from Smooth-on pretty regularly at work and think it would be a good choice. To choose which density, I would figure out the volume of the cavity you want to fill and then determine how much weight you are willing to add to the stock. The volume x density will = the added weight. The stuff will stick to just about anything. I pour it into UHMW molds and still have to use a release agent.

With that being said, I have never tried it on a stock and would hate for you to mess something up on my suggestion. I think it will work better than the canned foam based on my experience with both, but it's easy for me to think when nothing is a stake
smile.gif
Good Luck!
 
Re: Filling the butt end of a polymer stock?

I needed to get some weight in an ADL stock so I used fiberglass resin to both glue in some old steel pushrods from a Trans Am and then added some wheel weights. I didn't drill a hole, I just removed the buttpad and poured. Worked like a charm for me, stiffened it and gave it some more weight. That was a different stock though, so I can't guarantee it will work for you.
 
Re: Filling the butt end of a polymer stock?

Isnt the buttpad screwed on? Just remove the butt pad and fill the void with deading material. i would not spray anything, maybe a shop rag, high density foam, etc. I have used a couple of small lead ingots wrapped in styrofoam sheeting to add weight and balance out a Remington stock, but sure you dont want to add weight to a hunting rig.
 
Re: Filling the butt end of a polymer stock?

I removed the butplate pad from my Dick's sps and put in a loafbread bag and filled it with sand. Tamped it down a couple times. Filled just short of full. Had to use a little pressure to get the butpad seaded. Worked great. A little weight and a lot deaded sound. And can be removed at any time.
 
Re: Filling the butt end of a polymer stock?

I added weight to a SPS stock by inserting a ziploc bag into the void under the buttpad, then pouring in steel shot until the bag was full, and sealing the bag before reinstalling the buttpad. That way, I could still remove the shot if i wanted and there were no permanent modifications to the stock.
 
Re: Filling the butt end of a polymer stock?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Frank</div><div class="ubbcode-body">I removed the butplate pad from my Dick's sps and put in a loafbread bag and filled it with sand. Tamped it down a couple times. Filled just short of full. Had to use a little pressure to get the butpad seaded. Worked great. A little weight and a lot deaded sound. And can be removed at any time. </div></div>

LMAO.
grin.gif
 
Re: Filling the butt end of a polymer stock?

Appreciate the comments. I'm thinking the two-part urethane foam may be what I want. My biggest goal is to lessen the @#$# cheap flimsy feel of the stock. I don't know how Savage thought it was smart to machine a full length aluminum bedding system and then put it in a stock made of thin flexible plastic that makes the plastic stock on their $149 Mark II feel luxuriously solid. Adding weight is fine, mostly for slightly more rearward balance, not any attempt at bench stability. Hate to say it but after spending the cash for this in part because of the Accustock I am debating whether to toss the Accustock and get a $250 B&C stock, which is the same in concept but at least has the stock body made out of a solid material that doesn't feel like toy rejects.
 
Re: Filling the butt end of a polymer stock?

So I took the buttpad off to see what I would find, and it was hollow just as expected - except for a large piece of styrofoam taking up most of the space! Yeah, cheap styrofoam, clearly cut from a block outside the stock and pushed in there. Why bother? Why couldn't they have just poured something in place?

Anyway, seeing that I think I will try the two-part urethane foam. Jrm850, any more pointers on that? I'm inclined to use one of the heavier grades of foam, probably 8lb, to get the maximum stiffness and improvement in feel.
 
Re: Filling the butt end of a polymer stock?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SomeOtherGuy</div><div class="ubbcode-body">So I took the buttpad off to see what I would find, and it was hollow just as expected - except for a large piece of styrofoam taking up most of the space! Yeah, cheap styrofoam, clearly cut from a block outside the stock and pushed in there. Why bother? Why couldn't they have just poured something in place?

Anyway, seeing that I think I will try the two-part urethane foam. Jrm850, any more pointers on that? I'm inclined to use one of the heavier grades of foam, probably 8lb, to get the maximum stiffness and improvement in feel. </div></div>

I would fill the cavity with water until full, then pour that water in a measuring cup so we can get an idea of the exact volume. This will help avoid mixing too much and give us an idea of the added weight. I have a chunk of the 5lb in front of me but I'm having a hard time finding words to convey the material properties. I can only dig my fingernail in it about .030" so it's much stiffer than standard packaging grade polystyrene. This chunk is a 3" cylinder and I can stand on it with very minor deformation. I weigh 225. Obviously the heavier the better for your major requirements. I would come up with a number for whatever additional weight you can stand and pick a density to meet that number.

this stuff will stick to just about anything so make sure you mask off your entire stock before filling. Use a much bigger cup than you think you will need when mixing. Mix it fast and thoroughly. You have a very short pot life before it starts to grow. I fabricated a small mixer paddle to use in a coordless impact wrench. (Spins faster than the drill) I would mix a small batch and pour it into a cup for practice just so you know what you are dealing with. You can trim it with a knife before it fully cures but it's tough to trim after it's cured. A sureform file makes quick work of the lower densities when you go to remove the muffin top.
 
Re: Filling the butt end of a polymer stock?

I didn't bother reading the responses so if this is redundant I apologize.

Spray foam is a horrible idea. It doesn't cure. It dries. You can't get air to circulate down in your cavity so it's just going to sit there like a big old booger.

What you want is an epoxy that'll act like a foam. There's a few ways to go about this. West Systems makes a whole menu (daunting at times) of different additives for resins that work well in the gun world.

The one that I've used with great success for exactly what your talking about are called "micro balloons". They are little cornmeal/dust sized particles that will make epoxy swell up like a loaf of bread on crack cocaine when mixed and contained inside a vessel. Be aware, the stuff won't do much at first. Not until it starts to activate the hardnener and builds some heat. Then it's going to go like gang busters. It's all relative to the volume of material you pour into your stock. If you fill it to the top, be sure to mask EVERYTHING/ANYTHING on the outside, cause it's going to erupt like a caldera.

It'll do exactly what your after though and it'll stay relatively light and have some structural tolerance to compression and shock.

To increase the weight, add heavier material to your mix. Lead shot will turn it into a sled. Takes some of the snort from recoil out of it too without the slushy feel of a merc-tube.

Built a lot of light weight hard hitting silhouette guns this very way back in the day.

Good luck.

C.
 
Re: Filling the butt end of a polymer stock?

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Most guys will glue on recoil pads to hollow butt stocks.
That is mickey mouse. Glue in tension. Shame.

So I used to cut off some of the butt, dig out some of the foam, and put in a piece of Pine [light and unlikely to split] in the butt with a wood screw or two to fixture the position. I then epoxied it in place and the planed it off flush before screwing on a recoil pad.

I now leave the stock long for shooting prone, so I no longer cut off the 14.5" finished pull.

I now screw that Pine butt plug to the recoil pad, put epoxy on it, and hold the butt plug in place until the epoxy cures with surgical rubber. I put the curing stock on a heating pad. [Shown with the blanket unwrapped]

So no more sideways screws in my butt plug act.
No more planes.
No more cutting off.
It is long, flat, and flush when it gets hard.
 
Re: Filling the butt end of a polymer stock?

I come form the collision repair business so here is what i did on my HS stock on my rem 700. I filled the hallow part of my but stock with a product that i use daily. 3M 4247 Super Fast Plastic Repair, this stuff will stick to most plastics and fiber based materials, and as the name implies it kicks REALLY fast 30 seconds. Fill the cavity just above the end of the stock and let it cure completely. About 3-5 mins. then sand flush to the end of the stock. this stuff also works great for attaching the recoil pad. The down side is its about $25 for 200 ml and you need a Automix applicator gun to use it. if you have any autobody friends ask aout it. Just a thought.