So I purchased a new, never fitted B&C sporter stock for my 98 Mauser. It needs work. I think it's a '90s vintage model and doesn't fit my bottom metal very well at all. I've been catching short blurbs/mentions of "bondo-ed" stocks and even saw a Rem 700 stock for sale here recently with that mentioned in the description.
If my stock has big gaps around the bottom metal, is bondo the correct material for permanent repair? I think the receiver itself is going to fit just fine once I'm done fitting. I plan on fitting, pillar bedding, then painting and sealing. It's quite a project and I'm not totally looking forward to it but for what I paid for the stock I think it's worth it.

Any advice/experience is welcomed.

Thanks.

I used a full length Mauser BC for an intermediate length Mauser. I used Acraglass. That was 20+ years ago and it's still fine. I wouldn't use Bondo.

Thanks. I was thinking that a fiberglass resin of some sort would be a better idea.

I'd suggest a good epoxy filler for the inletting gaps you want filled. I'm working on a pattern stock right now and will probably limit using Bondo to adjust the external contours slightly. Someone more knowledgeable might weigh in on the chemical compatibility issue, but I suspect that the epoxy would be slightly more compatible with the stock material than the Bondo. You can add powdered metal or chopped fiberglass to the epoxy for more strength (if needed). I've used AcraGel on the internal part of the pattern stock and it sets up to an almost rock-like hardness over the course of five days.

I frequently mix sawdust with one of the quality wood glues (say, Titebond II or III0 and build up outside contours with that on wooden stocks. Cheaper than epoxy for large areas. Recoil lugs, barrel & receiver bedding, pillars - only quality epoxies.

Do not use Bondo to "build structure or do fitting such as bottom metal or correcting a larger flaw. For that a simple fiberglass (automotive) kit with matting not cloth will allow you to build up surfaces as needed to correct structure flaws.. Cloth can give a very finished surface if needed though. It sounds like you have some low spots in some areas that need to be brought up. After you have all contours and shaping done within a few mils and pillars and all metal test fitted but not final bedded you can use a Bondo skim coat to fill small imperfections that fiberglass is famous for or feather fill which is a high build primer made for fiberglass. Prime and paint as desired then finish bedding with preferred material (Acraglas. Steelbed, etc...) Some prefer to bed first then paint with appropriate masking. Good luck with this...

Marine Tex is also a very good medium for your needs and an excellent bedding material too you may be able to kill two birds with one stone with this and not need any fiberglass.

sell it and buy a good stock

Thanks. I don't think it's worth much with the work it needs.
I originally wanted a new B&C but the budget didn't allow it.
Had I known I needed to do this much work to fit it to my rifle I may have just saved up more for a new stock.

Marine Tex comes in gray and white and is an epoxy putty which is stronger than auto body bondo which IIRC is base on polyester resin. I've had good results with Marine Tex. Gougeon Brothers WEST epoxy brand is good too and they offer a variety of fillers to make putty consistency material. Just make sure you fill voids with clay and use a good parting agent.

Bondo is a cheap way to fill a big gap. Little structural integrity and poor adhesive qualities but you will only be out pennies for material instead of a buck or so you would have to invest in a a high end epoxy based bedding compound.

The money you save could buy you 1/4 of a small latte with only a moderate to high risk of job failure.

Brownells Acra glass or any good epoxy resin mixed with flock (ground fiberglass fibers) for structural areas that need strength. Mix it to the consistencey of cake frosting so it stays in place. Wet the area you are putting it with resin first to enhance bonding.

Anyplace you need filler but not strength, like under the barrel use microballoons instead of flock as its much lighter weight.

Before I knew better, I used plumber's putty and Elmer's Epoxy for purposes like this. Although it was wrong, I have to admit those mods are still intact after 35 years.

Acra-Glas or Acra-Glas Gel...done.
I think the gel is easier to work with.

Don’t over complicate things.

Leftybolt