I usually clean my P99 after 200 rounds fired so I wouldn't know about any problems after 400 rounds.
The German army and state police use the P99 as their sidearm (correct me if I am wrong), so they would have run extensive tests on the gun and would have rejected it if there were design problems with it.
Of course that doesn't mean you can't get a lemon every now and then.
All I will say is that I used to own a glock 23 and an hk usp before I settled on my Walther P99 QA.
The German army and state police use the P99 as their sidearm (correct me if I am wrong), so they would have run extensive tests on the gun and would have rejected it if there were design problems with it.
Of course that doesn't mean you can't get a lemon every now and then.
All I will say is that I used to own a glock 23 and an hk usp before I settled on my Walther P99 QA.