I didn't think airsoft guns had functioning slides. I remember nearly breaking the cocking handle on my friends AR-15 replica when I gave it a casual tug.
It depends on the maker, I can give the example of two M-4s, one had fully functioning parts (and was way more expensive), down to having to cock it and manually adjust the sites, and could use BB pellets as well while the other was a cheapo that was made of somewhat fragile plastic and wasn't really something that would last for any length of time.
It mentions in Silent Sinner in Blue that Reisen was extremely good with firearms as well, and you see other Lunar-bunnies practicing with bolt-action rifles.