Sounds like some chamber oil might have dripped into the pressure chamber of the rifle. You're gun is a spring operated rifle. They generate a tremendous amount of pressure and super heated air. Most of the time the extra loud reports will happen the first time you shoot your gun...and it will happen when you put chamber oil in the gun every 1000 rounds or so. Keep shooting and the sound should get lower after 3 or 4 shots. enjoy your new gun and good luck. I'm sure you know..NEVER DRY FIRE A SPRINGER. Didn't mean to yell, sorry.
You don't have to remember the truth