Neat experiment
That is an interesting experiment, but please help me to understand what really happened?
You say a failure to feed had to be removed with the cleaning rod? Does that mean it was in the chamber? It is my thought that a failure to feed doesn't get into the chamber. It is stuck somewhere between the magazine and the chamber, or it is still in the mag since the slide didn't come back far enough to catch the next round. I have never seen one of those that needed a rod to dislodge it.
If it failed to eject, then you had to remove it with a rod, that is failure to eject. No? I am confused. What happened for sure?
Yes, dirty brass and especially greasy brass may get stuck in the chamber.
I am not suggesting you shoot that kind of brass. What I am referring to is brass that is darkened with age. It must still be clean and free from oil and mud, gunk, and green patches, etc. However, I have been reloading for close to 40 years and never had a tumbler until just 2 weeks ago. I have never had a problem with dark brass as long as it was clean. A good wipe with a cotton rag takes care of the gunk. If it is green, a little steel wool will clean it up. However my brass never gets green unless it is something that has been lying on the ground for a year and you find it.
I guess my point is that you do not need a tumbler to be a successful reloader. You do need to pay attention to detail and wipe the brass clean. Don't let the lack of a tumbler hold you back from enjoying the hobby.