If you want a proven 20k rounds out of a barrel only one that comes to the front of my mind is the filthy 14 ala BCM/FN. Can nitride withstand 20k rounds? Certainly glocks with that many and more. I'm not a scientist but the research indicates the tennifier process used by Glock is almost if not identical to what we now refer to as Melonite/Nitride/QPQ.

The real question isn't what barrel can spit out 20k rounds, but which BCG can withstand that many rounds WITHOUT repair. In that regard the hunt goes on.

Whale Jizz hehe :)