I'm getting a rifle with a lightweight FG stock which was never properly inletted for the action. There are gaps in the stock to metal fit throughout. The stock was also never painted.
I'm thinking I'll use AcraGlas Gel for the action area first to establish a solid bed.
I'd then like to fill the gaps in the barrel channel with a much lighter material. I'm thinking regular AcraGlas mixed with microballoons to reduce the weight compared to solid epoxy.

Is there an alternate lightweight material for filling the barrel channel which sands and takes paint well?

Lightweight body filler perhaps?

What's worked well for you?

Light weight is paramount since this is to be my walking rifle and the weight is the reason I purchased a small LH Kimber 84 in the first place.

I did microbaloons one time and it worked well

I've used microballoons in low viscosity epoxy (aka syntactic foam) for all kinds of filling jobs and it works well. You do loose strength the more balloons and less epoxy so you might want to make up test batches if you're going for the maximum amount of balloons. Depends on the products somewhat but the standard recommendation is to add balloons until you get to a stiff peanut butter consistency. You can add more balloons before you really begin to loose strength, that's where you want to make test batches. That includes impact resistance which I should think is your main concern. The stuff gets brittle when you push the balloons. But the weight savings between normal and maximum balloons would be tiny unless you're building up like half the stock. On the plus side the more balloons the easier the sanding.

You want to apply a thin coat of plain epoxy before the balloon mix as the mix is pretty dry and won't want to adhere. Must be thin, too much epoxy and the mix will slip and slide when you try to apply it. You just want to make sure the substrate is wetted with epoxy.

There are commercial products that are variations on this theme, usually relatively expensive. Be aware some use different fillers like talk and can get heavy fast. Can't tell you about those with polyester resin as a binder. Epoxy is considered a superior binder if more expensive and a little harder to work with. I haven't done projects where cost is an important factor so I stayed with epoxy. (Except for Bondo when weight and strength didn't matter, the stuff is handy.)

As an aside epoxy with cotton floc makes a very strong, abrasion resistant filler or coating should you need it, but it is heavy.

Thanks guys.

Excellent info!

I have tried body filler, as well as metal body filler. if trying to get a small sculpt in the palm, it would be ok, any place that sees recoil impact will cause cracks over time.....at least mine did.

West Epoxies [see boat repair places] makes a good epoxy in two parts that, when mixed with micro-balloons makes a dandy filler as well as a good stable base for the barrel. Be SURE and use your release agent on the barrel and anywherre the stuff might ooze.
Aloha, Mark

Epoxy doesn't stick to polyethylene so anything from kitchen wrap to contractor's plastic works where you don't need up close and personal as with bedding. Can use it on top of epoxy to leave a smooth surface too.

Have had good luck with that 5" (?) stretchy plastic that Menard's sells on a roll with a handle, meant for bundling stuff. Wants to wrinkle but handy for protecting areas where you don't want any epoxy. Black plastic electrical tape (PVC) is my favorite though.

Once again guys, great info.

Once I get the stock in hand I'll assess what I'm going to need.

If it is really a wide gap then foam can be used with an epoxy skim coat over it. This is for non structural areas like the barrel channel. Test before hand for compatibility, some foams will react to the epoxy.

West system epoxy is indeed good stuff , but there are store brand two part glasses , that cost half as much and are just as good !

i've filled in several barrel channels with bondo with micro ballons. used duct tape on barrel to establish clearance, if put on carefully it will go on any barrel contour without wrinkling

Ed

No, that is not true. West makes a number of very specific epoxies and the standard Devcon. etc. blends do not match them for specific uses... In many cases they are not close.

But you may not always need the better epoxies and the hardware store crap may be perfectly suitable for your needs. No quick curing epoxy can hold a candle to slower cured proper mixes.

Devcon 60-minute is pretty marginal for example as bedding compound, just as Marine-Tex white is far more brittle than the gray.