yeah i have a Walther LP53 which i used for trial and testing all my mod materials and designs for both piston heads, top hats and guides.
Mainly because it has a large diameter piston which is incredibly easily accessible and where one can nip in out in seconds with each change made.
....but this gun evolved in its own right to a 500 fps super smooth shooter with no twang.
Later shortening the barrel to a K version .....
I also have a FWB SPort MK 1 which has been up rated with modern tuning techniques ....a keeper prob for ever.