!!!THIS MOUNT IS NOT VERY ACCURATE AND FOR SHOOTING 300 METERS WITH IT YOU WILL NOT HIT GOOD AND HAVE A LOT SPRAY!!!
In general, it is nice to have. But you will have more fun with a full metal scope mount. I tested it for 300 meters and I had a spray of about 60 cm on the target.
I think you still have spray due to the deformations of the plastic itself. And from every shot the recoil moves the mount a little bit and your scope isn't centered. You can print a lot of things, but not everything. Even though I had to learn this the hard way it was still very interesting to do and I had a lot of fun designing and testing it. Also it was interesting to see the 300 m target with 24x.

With this scope mount, you can still aim through the iron sight, the ejecton port isn't blocked and it isn't hurting the parts of the K31. The picatinny rail is 20 mm.

Important: Make for the section around the screws of the main part a 100% infill. The holes are 35 mm long. I made the 1x1 cm section with 100% infill around it as you can see in the .3mf file.

I used 6x 40 mm M5 screws for holding the main part and the bottom plate together, plus I think it was a 50 mm M6 for the screw in the middle. This screw replaces the K31 standard screw there. It is there so the scope mount can't go forward and backward.

Put some cork or a similar material between the bottom plate and the K31. Also stick some felt or similar to the sides of the main part (like you see in the picture) to not hurt the wood.

I used a M5 thread cutter for the holes in the main part where the screws fit in.

It is important that you first tighten the screws on the right side of the K31, after that tighten the screws on the left side. Then switch again to the ones on the right side to tighten them again. This is important because otherwise the flat surface on the main part isn't touching the receiver and then your whole assembly is tilted.

As scope I used this one from AliExpress, 6-24x50 with 20 mm: https://de.aliexpress.com/item/4000015814811.html
The quality of this is really good. I couldn't even believe myself that I get this for 36 bucks. If I would tell someone that this cost $1000 everyone would believe me. This has the real price of manufacturing and not the extremly overpriced shit that is made in the same factory from China but sold for over $600.

Bambu Lab X1C

Yes

No

0.20

60%, 3D Honeycomb (or something else you know is the best infill for strength

Drill a hole with a 6.5 mm drill bit where you want to put the screw through which goes to the chamber.

Here in Switzerland, a scope mount for the K31 starts at CHF 150 ($165) and goes up to CHF 300 ($330). Really? 200 bucks for a piece of metal? And the ejecton port is blocked and I can't use the original iron sight? No, not for me. So I designed it myself with my own important aspects that are:

1. Aiming with the original iron sight has to be possible.
2. The ejecton port must not be blocked.
3. The original parts of the K31 must not be hurted, especially no drilling in the metal and protecting the wood.