kx, I have never seen steel pellets. they have the non lead but it isn't steel I don't think. Most "springers" are not designed to fire bb's and do not have the magnet on the "bolt" that pump up kiddy rifles have.
They are all pretty loud but usually it is more of a "bonk" sound rather than the "CRACK" of a firearm... The exception is with excessive oil behind the pellet or in the cylinder section. If it is present, the rifle can and does "diesel". This is exactly as the name implies... The compression of air reaches a high enuff ratio that it actually ignites the oil just like a diesel engine does...
At this time, it will sound like a .22 or larger complete with smoke out of the muzzle. At night you may actually see the "muzzle flash".
Many of these rifles can be damaged if this happens so it is not wise to do it intentionally.
Brent