I've used 2 types of pellets - Crossman pointed and Crossman wadcutters.
The wadcutters fit better but last time at WW they were out. I'll see if I can get some of the Walther pellets.
Did your CP99 come with 2 backstraps? mine did.
The CP99 feels a tad large for my grip with the smallest one installed. I don't know how these compare to the backstraps that come with the P99 but I know it has 3.
I've been looking at buying a P99 in 9mm. The firing range I go to rents HKs and Glocks, but not Walthers. So, I've shot the USP Compact and Glock 19 for comparison and ruled out the Glock. I haven't found a P99 that I can shoot just to make sure.
I know the CP99 has the same dimensions as the P99. I love the way it feels in my hand - very comfortable. I'm also interested in the recoil as I want my 13 yr. old son to be able to shoot it. The USP Compact is a bit too much for him.