I started by sanding it down with 60 grit sandpaper to make the paint more easily adhere to the resin. Then I migrated out to my garage and went to my trusted Rustoleum spray paint. I sprayed a coat of bright silver over the entire gun, making sure to get into all the nooks and crannies, let it dry, flipped it over, and did a coat on the reverse side.
From there, I started doing more research: pictures, information, and finding all the necessary things to delineate this gun from a real one (a half inch orange tip on the end of the barrel is customary). I found some pictures helpful, and others not as much, so I chose one that was the original, and one that I thought would have the best detailing that I could duplicate - duplicating a metal look on resin isn't quite as easy as it sounds.
After I had the detail mostly done with the top half, I moved to the stock of the gun, where I broke out a second paint color - this time red - to make the wood look. I didn't use the rag nearly as much on the stock, this way I could make it look more wooden. I added some browns to give it depth, and I hung it from the trigger to dry.
After a few hours, I did the orange tip to make sure the gun could be distinguished from the real thing and left it to hang overnight.