Thanks guys, very helpful.

Do either of you know the H&K RC heat treatment?

I seem to recall that the standard US 4150 was RC 32-34, whereas the H&K was RC 42-46?

I'm a pocket knife nerd originally, prior to getting into guns. Thats an area where steel and RC harnesses are both tremendously important to overall edge retention. 

So I imagine that using a harder RC treatment would also factor into overall 'rifling retention.' 

For example, a typical bayonet is 51-53RC vs 59-61 for a modern, high end pocket knife. That doesnt seem like much of a spread, but theres a huge difference in overall edge retention. Even the difference between 57 and 60rc is noticeable on a pocket knife.

That's about right.

I'm still not in the clear of why they decided to go with Haenel's AR aside from the rumors(?) that it's supposed to be a cheaper alt. of the 416.

I thought the bundeswehr have already fond of their 416. And The 433 might be more pricey but it got a lot of new features and improvements from the G36. Did H&K messed up in the run somewhere? or did the Haenel and Caracal just have a more powerful political power?
 

52mio Eur cheaper is a huge chunk on a 250mio Eur deal, the problem is if that saving is mostly down to creative accounting in regards to firearm life span  being longer due to that replaceable cam thingy.

Just for the record [don't take this as my statement of supporting the selection]:

A more or less official statement sadi that the Haenel weapon fulfilled all requirements and was "over the expected lifespan" cheaper than the competition.

The 52 million EUR figure cited in this thread does not show up in any official statement I am aware of. I have no idea how close it is to the truth. 

I guess this channel will be interesting for you:

https://www.youtube.com/channel/UC6htLMymL0WJSNe109iBU1A

grand-grand-grandfathers of pocket knifes aka navajas

I'm trying to fully understand the role of a replaceable cam in extending rifle's lifespan

Would you be (or anybody) be so kindly to develop it?

An AR-15 does not have APE which means the interior of the aluminum receiver stops the bolt from locking prematurely. Over time the wall of the receiver at the cam pin location wears out and the upper has to be replaced.

The wears could also be minimized by using a roller cam pin. Then again it's patented stuff so companies don't go around making one.

Wonder why E. Stoner made the cam pin rectangular instead of smooth rounding in the first place.

The roller isn't in patent. There are Armalite guns from 1960 with roller cam pins.

It's ultimately unnecessary and adds cost, which is probably what they were thinking at the time (would have been Sullivan and Fremont). However I agree a roller is an improvement. My guns avoid this issue entirely by using an APE rod.