Bruce, this whole Bruce this is an excellent piece of advice. Highly recommended. I hadn't heard of the magnet idea -- thanks for passing it on.
Your observation of the nasty lost fibres is soooooo very true. This is why in wooden boat restoration steel wool is a no-no. In a salt environment only a day of exposure and the black marks of rusted metal on wood are evident. And they are extremely hard to remove, except with oxalic acid or intense sanding. Boating stores all sell bronze wool for this very reason -- bronze doesn't leave black marks.
In the same vein, I concoct a mixture of 50% bees wax 50% petroleum (mineral) jelly (a formula taken from the 1931 Enfield Armourer's manual) and coat the all wood where iron/steel contacts wood (drawers, barrel channel, butt plate screws, etc.) not only to prevent the black plague stain but to keep screws from rusting in the wood and becoming neigh on to impossible to remove years later. It also acts as a barrier to prevent gun oil from invading the wood and creating spongy oil rot (especially important in the drawers). (as a double entendre, this wax balm is great for furniture drawer slides, better than soap or candle wax).