Glass bed or fiberglass Bondo hollow shock fill?

[Jak300gt]

I've read where people are using bondo to fill hollow stocks. I'm wondering if it would be better to use glass bedding instead. I recently picked up a Mossberg ATR and I am planning on filling both the butt and forearm to add weight. Yes I want it heavy for recoil control for my son. After I fill the major voids I plan on bedding the action. So then the question would be would one stick to the other. Has anyone tried either of these and how was your outcome?

[tobnpr]

"Fill" to add weight, I'd use an epoxy like West System with a high density filler to add weight (you could also add other material like steel shot)- usually it's just the opposite- trying to shed weight, not add it.

Rule is that epoxy resins will bond to polyester, but not vice-verse. After a certain period of time (depends on the exact product), even epoxy-to-epoxy will need to be sanded first to create a mechanical bond if cure time has been reached.

Epoxy doesn't get a good-if any- chemical bond with polymers. So if it's a polymer stock you need to de-grease the stock thoroughly, and rough sand all areas to be bedded, and I always drill in some reverse "divots" into the stock that the epoxy can flow into to create a mechanical lock. If you don't, it'll likely just pop loose.

After I fill the major voids I plan on bedding the action.

Do the receiver and forearm bedding at the same time, why make it two processes given that you can use the same material (high density/strength) for both applications? I'd need to have the stock in my hands to know exactly how I'd do it- but you could either lay-in a "spacer" in the forearm to float the barrel, or just bed the barrel along with the action (plenty of release agent!) and then sand it out after to float the barrel. High weight/density epoxies don't sand too easily so I'd keep that to a minimum.

Be sure to do this thoughtfully, so as not to adversely affect the weight distribution/balance of the rifle.

[uwmac]

If weight is your goal, bedding compounds or Bondo are neither the most dense material. If I were tackling the same task, if look for steel, or other weights to epoxy into the stock system. Mercury dampeners can be installed that do more than just add weight. With the proper mechanical locking geometry, epoxy and Bondo will bond, it's just not a preferable thing to do to a good firearm.

[HiBC]

A serious problem you are likely to run into if you pour that stock full of epoxy is heat.

Epoxy,like most plastics,polymers,etc is a poor conductor of heat.The When you add the catalyst,it starts producing heat.In thin cross sections,the heat can dissipate.In a thick section,the heat builds.The heat accelerates the cure rate,and it becomes a chain reaction out of control.Smoke,fire,etc.

You can test this by just mixing a 2 OZ batch of resin in a cup and letting it sit.I suggest outside on a non combustible surface.

For what you describe,I suggest building in a chamber or two,maybe buttstock and forend,where you can place(or remove,later) some form of metal weights.

For actually filling the hollow void,I suggest an expanding urethane closed cell foam,as is used for marine flotation or insulation purposes.

[T. O'Heir]

Bondo cracks and falls off under vibration on a car. Glass bedding material is epoxy with fibreglass filling. JB Weld is the same thing with steel dust in it.
Be less fuss to replace a cheap hollow stock. $129.00 for a long or short action from Boyd's. An ATR is a Model 100.
"...chain reaction out of control. Smoke, fire, etc..." There's no fire. Gets hot though. Really exciting(moreso when you're new at it. snicker.) but not in the least bit dangerous as long as you don't touch it. It's just a chemical reaction.

[5whiskey]

Much to everyone's surprise, I have used bond-o with much success on synthetic stocks. I have bedded a few actions with it (must sand and drill multiple opposing angle holes to create a mechanical lock, as previously mentioned), and completely reshaped a stock by adding bondo to the forend, grip, and comb of a stock. It's held up for 9 years. I used bond-o because I had it on hand, really. Since I have used Acraglas as it's more "professional," but there is no difference in durability and function. You will have to thin the bondo a bit to get it to flow where you need it, and it's slightly more difficult to work with than Acraglas, but there will be no accuracy nor durability difference between a rifle bedded with one versus the other (all other things being equal).

I believe Bond-O is slightly denser than a glass bedding compound, but not enough to really tell a noticeable difference. I like the idea of adding a dense filler to whichever compound you choose, possibly steel shot, if your goal is to only add weight. BTW, You will not need to, nor want to, fill the entire stock with epoxy. Nor would it ever cure if you did.

[Jak300gt]

Thanks everyone. I believe my question has been answered. I was worried about the heat and planed on doing it in layers. I was aware of Boyd's stocks but my son is set on wanting to paint it camo and I can't bring myself to paint a brand new wood stock.
Also I have thought about the balance of the stock. I'll have to measure the volume of the voids I plan on filling and try to match a stock I have for another rifle.
Thanks for the idea of the recoil reducer that would work good in taking up space and better job of recoil management over just adding weight.

[uwmac]

The heat phenomenon is called cross linking, and is driven by added/engineered to occur because it drives the reaction necessary to form a long and very strong and stable chemical chain. There are lots of options to keep this from stopping you if you are set on this method including planning a method of cooling. There are even some epoxies that require you to supply a hot environment to cure them, and those may be better for your project. As a rule of thumb the shorter the pot life the more heat is generated by large masses of epoxy products.

If this were my kid, I'd put money toward a muzzle break, and plan weight distribution differently. look at components like bipods,scope, and mounting bases and rings tactical picatinny rails and rings made of steel will add lots of weight nearer the balance point of the rifle you will get a more functional product for your kid than filling goop in the stock. Just a suggestion.

[Dixie Gunsmithing]

You can get recoil reducers that are clamp-on, or are placed inside the butt of the stock, which have either mercury, lead shot, or a spring loaded weight in them, that can help counter recoil. I'm not sure that they manufacture the ones with mercury anymore. Anyhow, the internal weight, inside the tube, moves in the opposite direction, (actually the weight stays stationary, and the tube moves rearward with the gun), under recoil, which dampens the felt recoil.

[T. O'Heir]

"...a brand new wood stock..." There is that, but Boyd's stuff is laminate. Anyway, on any synthetic you're painting, Krylon is your friend. Relatively inexpensive spray paint and they make colours specifically for camouflaging stuff. Home Depot.

[Slopemeno]

How about filling the rear of the stock with BB's or steel shot before doing something more permanent?

I have my own epoxy story. I landed one of my super-heavy r/c sailplanes and managed to hit the only rock in the LZ, so I thought "Ok, I'll just roll a cone of mylar over the broken nose and pour some Tap Plastics Super-Hard 4-into-1 epoxy in from the back, let it cure and remove the mylar. So far, so good. So I mixed up way too much epoxy- maybe 2.5 to 3 ounces- in one of the those red party cups. I poured the mixed epoxy in from the rear and left the plane nose-down so it could cure, and went back to watching the TV.

A minute later...What's that smell and sound? It was the remaining contents of epoxy in the party cup boiling and smoking. I grabbed the cup and ran for the front door of my apartment- the bottom of the cup let go just and I got out of the door, and the glob of epoxy is still stuck to the walkway outside that apartment 20 years later. I never did get my deposit back.

That solid epoxy nose is still holding up too. Tough stuff.

[Blindstitch]

I filled a shotgun with sand and that seemed to work ok and was reversible.

Collect some sand.
Place a bag inside the stock.
Fill the bag with sand.
Tie off the bag.
Screw down the stock plate.