How I would fake the no shell casings. Let’s just say the rounds and bullets that fired outside at the gate are real. Just to keep it simple. What I would do, is lay a video or even just and image to the right over the footage. Put a bit of blur to make sure the bottom feed video and top layer look like they match. Presto! Bullets disappear before hitting the ground. This isn’t even Hocus Pocus good skill editing. It’s just simple layered image work.