wanting to add a picatinny rail to my Diana Airbug but nothing to be found. So i came across something similar but for a Crosman. I just printed that file and checked if it would fit. It did not. So i opened Tinkercad and sliced some stuff off.

I printed this in a copper PLA standing up. No supports needed. It's a really tight fit, so i would suggest a little sanding on the inside. I did a 25% infill and it toke around 2.5 hours.

This would probably fit a lot of DIana airguns. Just try it out, i think its worth the time :-)