A quirk I noticed with every weapon is that the spent casings don't seem to properly despawn.
When they hit the ground, they make a sliding sound like many props, and the sound does not go away at all until the admin cleans up all. What makes things even more confusing is the casings are completely invisible as well, I only figured this out on flatgrass after using them there.

This bug's been reported a few times now by others at this point, and as of writing the last update was in 2019. I'm holding out for a fix, these are the most authentic CS 1.6 weapons the workshop has on offer.