I should also mention that my non-reinforced early model K9 has seen primarily +P and +P+ rounds. I would venture to say that 90% of all rounds that I've put through it were marked +P or +P+. I started off carrying my K9 with Corbon 115gr +P JHPs as this was, from what I read at the time, the cartridge Justin Moon designed the K9 around.
Later, I switched to Georgia Arms 115gr +P+ Gold Dots due to the price and put a good many of these through the K9. A few years later, I decided I was more accurate with 124gr fodder so I switched to 124gr +P G-A Gold Dots. A few hundred rounds later, I stepped up to Winchester's RA9T (127gr +P+) as I read it was the cat's meow and stuck with it until I ran through what I had (only 500 rounds).
Since then, I've switched all my 9mms to RA9124TP since it has proven to work well from the K9, UC9 and Hi Power and the price was right. My K9 has seen a many rounds of RA9124TP with no complaints. I'll likely stick with this for some time longer as it's competitively priced and seems a bit easier on my pistols than RA9T.
On rare occasion, I will shoot some reloads of moderate pressure though the K9 in attempts to be easier on the wallet, but for some reason I can't get the accuracy from my reloads that I can from factory ammunition (which isn't necessarily the case for my UC9); a mystery left unsolved.
The only thing that has been changed out is the recoil spring and only because I thought it was about time to and not due to function.
As svelte as it is, the K9 is no doubt one robust chunk of ordnance steel.