But that's not really the parts that put out metal shavings...
The steel cams are riding in aluminum bearing ledges. Which of those two parts would lose material...
The piston rings are on aluminum pistons in an alusil sleeve, not gonna lose much steel there either.
Lifters are really HVA's and are fully stationary in little holes, not moving parts.
The valves ride in guides made of softer metal as well. (notice that all the steel parts ride in softer metals)
If your valve springs or retainers are losing material there's much bigger problems in your engine!
And I have yet to hear of a case where rod bolts/main bolts etc. lost material...
The oil pump itself is simply the best lubricated part in the engine, and the only time I've ever seen a BMW oil pump fail is when they busted the oil pan and drove without oil... but no worries, the new engine came with an oil pump already installed.
The only parts you mentioned that can contribute to metal shavings in the engine are the rings and the chains/sprockets... and I have yet to see a chain worn down, or sprockets at that, in one of these modern BMWs.
But hey, you did find steel in the engine!
As always, the best bet is to just use proper oil and filter, change at regular service intervals (or sooner as many of you do) and keep up with your basic maintenance. Minimize the conditions that cause engine wear/shavings to begin with, much better than something to merely collect the shavings.