I did not much like the original baffles on my P15 so I designed my own. These should also fit the P12.
These are a little bit taller than the stock ones so you probably only want 7 of them and move the shroud holder some 4mm forward. If you insist in having 8 of them you will need to move the shroud holder some 16mm forward. You can see in the pictures how 7 of my baffles compare to 8 of the stock ones.
The STL shared is designed for .22 (5.5mm) pellets. It will be ok also for .177 but might clip for .25. If you own a .25 version you may want to make the hole a little bigger.
Physically the hole should be around 7mm and is big enough for the 6.35mm pellet to pass trough but the bore of your barrel is not necessarily perfectly concentric with the shroud and you may get clipping or big POI drift.
In my .22 P15 these baffles work very well and quieten down noticeably.
Note that they are a tight fit and need to be pushed down the shroud with the help of a wooden dowl.