Putting a dent in a dentless helmet is possible, but not as easy as others have said.
First thing. really look at all the reference photos available and make a layout on your helmet. The dent size actually does matter for accuracy, since you want 501st approval.
After you have done the layout, you will have to contour thorough the helmet shell. The dent is deeper than the skin thickness of the helmet for sure. Its a dent, not a scuff or a gouge.
Best tool for that cutting and contouring, would be a series of Dremel cutters and sanders, with hand sanding to finish.
Now you are going to have a big old oblong hole in your helmet. Using a hand made contoured shape from the outside, (buck/form) of the dent made out of something like contoured balsa with a release tape shell. The shape will be stuck into the hole like a plug of a leaking boat. Tape it down in place from the outside so it stays plugged.
Now comes the fun part, do 2 layers of FG chop stand mat with resin. (The inside of the helmet will need some sanding first to leave a key for the new resin to adhere to). Once cured the buck is removed, and you will have a basic shape of the dent. After some body work, the dent shape should come out looking like the photos.
Only then could you apply a thin coat of cold cast resin to try and blend in the original cold cast layer. Allow to cure and buff under cold water with 0000 steel wool
Sounds easy right? Well the problem is that there are different brands and mesh sizes of metal powder on the market. Then you add in the variables of resin types, brands, humidity and temperature, all the more unlikely to have a seamless finish.
If I were you I would just Keep the ASOK helmet in my collection, and get a second dented helmet and finish it. Painting a Jango helmet is not difficult, and your out of pocket costs will be around $315, with paint supplies. If money is tight do this dead last.
