A friend of a friend picked up an older Marushin 1911 with the shell ejecting feature, it's neat but the shells themselves are discontinued. I modeled this off of an original shell to create a simple design that could be used for spares.
This should help people who plan to use these Marushin shell ejecting airsoft pistols in a field environment, as shells printed in PLA will be cheap to replace and will bio-degrade if lost or forgotten. You won't have to spend an hour picking shells out of the grass, or spend the rest of the day after a game staring at your loadout depressed because you lost 3 of your original, irreplaceable shells. As a result, you should actually be able to use your raresoft Maruishin instead of confining it to a display shelf.
This is version 1, which does not include the rubber retention ring present on the original shells. I had fiddled with an O-ring based retention system, but the O-rings required have a larger outer diameter than the shells themselves, so it won't work. As a result, you might be sacrificing some velocity using these.
Version 2 is in the works and will be a 2 part unit, with the bottom of the shell being printed from PLA and the top half designed to be printed from TPU or ninjaflex, so it'll have BB retention and seal similar to rubber while leaving the rim strong enough to handle the forces of the extractor mechanism.
Print from PLA at 80-100% fill density, if printing at 80%, change your printer program settings to make the first few layers solid fill, so that the rim is strong enough to handle the extraction forces.
For filament I recommend a high-visibility PLA, such as Neon green, orange or yellow. The color will make it far easier to locate shells dropped in the field, and printing them from PLA will ensure that any unrecovered shells bio-degrade in short order.