This was my first "big" print, but turned out pretty good. Thanks for the great design!
Most of it was printed in .2 or .24 layers using Overture PLA on an Ender 3 v2. I used filler primer and just a small amount of bondo to fill some of the gaps and smooth it out. I sprayed a metallic silver and then green on top so that I could do some weathering by lightly sanding some of the expected rough spots. Then finished it with some watered down black and painting it on in spots and then rubbing off with a rag.
I did modify the front chin piece and combined the 3 pieces and printed it all at once. That worked out well and saved at least a little glue time. I also used magnets (https://www.homedepot.com/p/Master-Magnet-0-47-in-Neodymium-Rare-Earth-Magnet-Discs-6-per-Pack-07046HD/202526367) to hold the chin piece on so I can easily remove it. My head does not fit into the helmet without the chin piece being removed. These magnets fit perfectly into the existing holes already in the design of the helmet and are 3mm's thick. The holes are 7mm's deep so I created simple cylinders in Tinkercad to adjust where the magnets sit. On the chin piece I created a spacer that was 5mm deep, glued it into the hole and then added the magnet on top. It protrudes just enough to sit inside the hole on the helmet side to ensure alignment. On the helmet side I glued the magnet in first and printed a 3mm spacer to glue on top. This reduces the strength of the magnets just enough to keep it secure, but still easy to remove. You'd probably be fine having it magnet to magnet, but these things are really strong and I didn't want it to risk ripping the magnets from the glue when taking it off.
I also inserted 4.1mm spacers (slightly longer to make the magnets stick out from the holes just a tiny bit) and then magnets into the 4 holes on the inside of the visor and have the face shield held in with other magnets on the back.