Get a good pair of muffs and a soft set of earplugs as well. Wear them both.

You might start with a .22 and work your way up to the larger calibers.

Always wear hearing protection while shooting. Especially on young peoples ears. Once you lose hearing sensitivity, you will never get it back.

Depending on the powder capacity and mass of the projectile, a supersonic "crack" can possibly be louder than the "blast" shockwave of the expanding gases from the barrel.