Saw this on Shooting Illustrated...

Thanks for the chart, the loudest gun I fired without muffs on was a .45 auto, to be honest, the worst gun to fire without muffs is a .22lr, you don’t think it’s loud, pretty much it really isn’t, but the repetitive shooting causes the damage, I know from experience, I never used muffs for a .22, now my left ear has tinuitis. In a self defense situation, I think adrenaline will take over and you may not notice the noise from shooting inside, just my thoughts.
Wait until you shoot a 22mag inside! Just don't!