I have some .50 cals I bought, what is the best glue and paint to use with these?
I have no experience with the plastic used by 3D printers, so I don't know what is the best media to use, and or even if a 3D molding will hold it's shape over time.

TIA

there's multitudes of 3D printer plastics out there. Any idea which one? if they were purchased thru Shapeways, there's forums on their site with all sorts of info.

If it is the Frosted Detail plastics (actually a form of resin) from Shapeways, then super glue/CA glue is best. Before putting down any paint, wash the part very well. Soak the part in acetone for a few minutes (I usually do 5 minutes) and then soak it in WARM, not hot, water with dish detergent for a few hours. Then rinse the parts off with warm water. If you have an ultrasonic cleaner, you can also use that to clean the parts. I've found that priming with a light coat of Mr. Surfacer works well and does help to smooth the surface somewhat.

Unless subjected to high heat (and I believe direct sunlight), the material should keep the shape for a while.

Actually, Shapeways recommends leaving the product under a UV light, or in direct sunlight, for an hour or two, to complete any curing process, otherwise it may not hold paint well. I always use CA to glue the 3D printed pieces.