it's not "Tin", FunkyZero, it's Polycarbonate. They make bulletproof clipboards out of one of the early polycarbonates that was a quarter inch thick for police use. I saw one demonstrated that stopped .38 Specials at point blank range back when I managed The Old Sacramento Armoury in the 1970s. Impressive. The manufacturer claimed their 3/8" thick model would deflect .357 and .44 magnums and had videos showing it being done.
These back cases of the iPhone 5C aren't that thick, but the individual pellets in the shotgun blast aren't the monolithic slug or a .38 either and individually don't carry too many foot pounds of energy..
Was the armoury actually located in Old Sac? I always liked Old Sacramento. We always took Jefferson or Harbor Blvd to Capital Mall, past Rayley Field, across the Tower Bridge, to the Capital building. I always got a kick out of that 2nd floor door to no where. Kind of reminds me of the Winchester House in San Jose. I liked the K Street Mall too. I still remember some of the streets, like Bradshaw, Power Inn Road, Howe Ave, Arden Way, Greenback Lane, Walegra, to name a few. Many of my co workers live in Sac, Fair Oaks, Elk Grove, Citrus Heights, North Highlands, Orangevale, Antelope. I bought my BMW at the Roseville Auto Mall. It all brings back memories.