Pellets are one thing, but I’m looking for “look-feel-sound”, so if say, you are firing a .38, it simulates that in every way except a bullet coming out and a casing ejection in an automatic.
Recoil is very difficult to simulate. At best you can make the action cycle with air. I've "shot" an M240 machine gun set up to do that, wearing computer display goggles as part of an immersive simulation.
The goggles/glasses have improved since then, but they made it impossible to correctly use the sights. Fortunately you could use the simulate tracers and bullet strikes to adjust fire.