[Ni3Frontier]

DirtyVicar,
What was this 'not quite right' feeling you got when you reassembled your P99?

How many rounds total do you have through your P99? I have not experienced this problem but it could be a worn recoil spring. Or was the recoil spring installed backwards?

I'm not sure how new your experiences with handguns is so forgive me if this is something you already knew; with a fully loaded 10 round mag you will need to give it a good thwack to get it in to the weapon with the slide closed. Think about how difficult it is to get the 10th round into the magazine. The top round will press against the bottom of the slide when it is inserted. To seat the magazine, the spring must be compressed further which can be quite difficult. You stated that with 9 rounds in the magazine it went in without trouble.

-Yoshi

 

[Ni3Frontier]

DirtyVicar,
I can't really think of anything that would cause this problem other than foreign material somewhere in the workings. Try cleaning and greasing the grooves in the slide and the lugs on the frame. Make sure the lugs on the barrel and the attachment point on the frame are clean and normal in appearance.
When you have this problem does your P99 have a gap between the slide and frame when it is assembled? In all honesty there really is only one way to put the P99 back together. I doubt you'd be able to put it back together without having the lugs on the frame seat into the grooves into the slide. Try disassembling and reassembling your weapon a few times to see if the problem happens most of the time or just occasionally.

-Hope this helps!
-Yoshi