I tried the shells available on here and found them to be a little to inconsistent. I ended up making these with a few changes to hopefully make them more consistent for use.

The base is a little thicker to help keep the air seal between the chamber and shell. The top of the shell should fully engage with the top of the chamber to ensure the bb leaves the gun centered.

I have provided a variety of different sizes in the file to allow you to test and tune your revolver. I found the 3.2mm was about the same as the brass high power shells and 2.8mm worked at around 360fps-330fps on a fresh C02 cartridge.

I have also included the dwg and fusion 360 file if you need to do some of your own tuning.