Airguns both pellet (for accuracy) or BB for faster action.
Airsoft if your pistol is one of the more "mainstream" models where metal replicas are available. Glock 17,19, Sig P226 and P320, Beretta 92 series, S&W M&P series, 1911. These are safer than steel BB's for drawing and shooting practice. But you can still shoot yer eye out!
But for ultimate realism, dry fire with your real firearm if you safety check safety check safety check. And if it won't damage the firearm. Laserlyte makes laser inserts into the muzzle and detection units that either ring, light up, or jump a little when you score a hit.
And by the way, with airsoft you can purchase an adapter cap and fill up with propane for cheap propellant. Forget "green gas".