I've re-made the revolver based on original EDUNBR3D's design implementing some changes for easier printing.

Changes from original:

• All parts were re-modelled with some improvements;
• A way the drum is attached to body is changed (it is more reliable);
• Made some changes for easier printing (require less supports);
• STEP files included.

I sliced in OrcaSlicer from STEP files using tree/organic supports.
You can see my support parameters on included pictures.
Notice, I adjusted threshold angle to 30 degrees (my printer can do this) and increased first layer expansion for organic supports. Without the last change the handle most probably will break while printing in 100%.
No support needed for drum, bullet and pin.

Printed on Elegoo Neptune 4 with 0.4mm nozzle using 0.2mm layer height in 100% and 150% sizes. I prefer bigger one as 100% is too small for me (it is ~82mm in length).

To check gaps/fittings I'd recommend you to pring drum and pivot first.
If too lose/tight and you use OrcaSlicer -- you can make adjustments using option "X-Y hole compensation" (I printed without changing the option, however my printer is quite good calibrated).
If pin is too lose -- just scale it up a little.

Assembling: insert pivot into drum, insert the pivot with drum into body and fix it with pin.

Demo and assembling: https://www.youtube.com/watch?v=9x2ETVtSSgQ

21 Feb 2024: Uploaded bullet's model as separate files.