Making new friends helped her 'come out of her shell'. = Making new friends 'brought her out of her shell'.
He lost confidence in himself and 'retreated/withdrew into his shell'.
The police found several spent 'shells' at the scene of the shooting.
(..) ...the Germans had an artillery piece... It's the biggest in the world. Called the Gustav Gun. And it weighed a thousand tons. And the Gustav was capable of firing a -ton shell... ...and hitting a target, accurately, miles away. I mean, you could drop bombs on it every day for a month... (..)2008 TvShow: Breaking Bad Title: A No-Rough-Stuff-Type Deal Season: 1 Episode 7