I noticed a small, rectangular, metal shim with a hole for an action/stock bolt. I think it fell out of one of my bolt action rifles when I removed the action/barrel from the stock., possibly from my Browning Abolt II?? I assume this would go between the action and the stock....??
Two questions...
Is this likely to go on the front action screw or the rear (near the trigger) screw that bolts onto the stock?
Why do the manufacturers put these in the stock? And what difference is it if I don’t have it in the stock?

Like #190 in this parts diagram?

https://www.brownells.co.uk/Schematics/Browning/Shotguns/Browning-A-Bolt-Shotgun-SchematicBrownells parts diagram

More than likely it goes between the bottom metal and the stock, check the fit between the metal and wood, I would bet the wood is proud

That was my guess as well....

Upon closer inspection, it is some type of plastic. Not sure what this came off of, but I am beginning to think it not one of my rifles.?.

https://www.24hourcampfire.com/ubbthreads/ubbthreads.php/galleries/14674650/plastic-shim

Well the picture shows it's not that, but any idea why Browning did include the tang plate on the A-bolt? Seems designed to act as a spring of sorts rather than as just a standard shim.

Looks flat in the photo, so if it did come from the stock/receiver interface of one of your rifles, it would probably be one with a flat bottom action. Can't say I've seen one like it, for what that's worth.

I have a Sako with similar shims between the bottom metal and wood. Not only is the wood proud, but the inletting is too deep and the shim prevents overtightening and binding the mag well.

Most of the Remington 700's I worked on had either a shim between the front and/or rear of the trigger guard and the wood . As far as I could see it was just trying to make poor inletting look better. Sometimes there were two.in the front to keep the screw from protruding into the receiver too far and interfering with front bolt lugs.
I can say I didn't see this ever on the 721's, 722's and early 700's.
Just a case of poor quality control as far as I could see. I did see them on on other brands occasionly.