https://www.youtube.com/watch?v=WcfqZFWpk9s
I've always heard they don't perform so well in dirty conditions, but never saw a demonstration. This video shows the Mini 14 both clean and in a dust test, also using CLP, grease, and dry. It's even worse than I thought.
The dust test seems reasonable, without being to the extreme that some of the youtube torture tests are.