I created this insert for the Colt Python revolver cylinder to visually indicate that there are no rounds loaded, and the firearm is safe for handling. There are two versions, one with 6 identical cylinder insert lengths and one with two of the cylinder locations that have a 357 Mag and 38 Sp dummy. Depending on the accuracy of your printer/filament, these two dummies are designed to be to the max dimensions per the SAAMI specifications. I printed these in PTEG and Hyper PLA and they held up well to range usage, going on 1 year of weekly/monthly use. The back plate is the weakest part of the design since it has to be thin enough to fit between the cylinder and the firing pin/hammer body. Enjoy.