The only source that I have found on the USA internet for rifle cartridge traps is the New England Gun Company. They have four versions of the usual type inletted near the heel of the stock, and they must be platinum plated.
I have a dim memory of seeing several WWII GI acquired drillings with cartridge "traps" in their butt plates.
Does anyone have any other sources for cartridge "traps" that I can purchase? How about plans? Maybe I could get someone in China to machine one for me?
And then who would you trust to install one, in/on your first (or next) SxS rifle?
I have picked up my first SxS, a 8x57JRS (not that common in the USA); so, I think having four spare cartridges at any time is not a bad idea.
By the way, I did not order the rifle; I bought at a discount "off the shelf". BUT,it has been on "layaway" in my mind for 50 years ... .