I am an experienced designer and airsoft player too. Hope to bring you useful 3D stuff.
If you are looking for well precise machined P-Hops (Precise Hop) patches from solid rubber contact me.
These patches are available in different sizes to fit to any barrel precise, the only thing you need is to cut the length.
Much more easy than the R-Hop from rubber hose. Installation within a few minutes and made from the most stable rubber HNBR.
You can see a lot in the German ASVZ forum, username scasso.
Special Levers for the patch are available or under progress