His other weapon, an AR-15 - the civilian version of rifle carried by soldiers in Iraq.
"You have to up the ante a little bit; you don't want to go to a gunfight with a knife," Caldwell told CBS News correspondent Kelly Cobiella.
Especially when the gun on the other end of the fight is an AK-47, favored weapon of terrorists and, these days, the common criminal - used to rob grocery stores and donut shops. Last month, one was used to shoot four Miami-Dade police officers during a traffic stop, killing one.
The Broward sheriff's office confiscated 25 of these weapons in a week's time. Two are versions of the AK-47. They're cheap, they're easy to get and they're powerful enough to pierce body armor.
Because of that, police are finding they have to upgrade their own arsenals. The guns usually seen in a SWAT officer's hand are now being given to beat officers in more than 20 departments around the country.
Miami's police chief is the latest to follow suit.
"I have an obligation to my police officers to make sure that they have an even chance," said Miami police chief John Timoney.
Yet in many departments there isn't enough money to arm the entire force. Many beat cops have to buy their own rifle at a cost of more than $1,000, while assault rifles are being sold for as little as $200 on the street.
Twenty five-year-old Grady owns both an AK-47 and an Uzi.
It can fire 600 rounds at the flick of a finger. In his neighborhood, Grady says it's the only defense.
"I need something that, when I pull the trigger, is going to spray," Grady said.
And it is set to automatic.
Caldwell knows a spray of bullets could be around the next corner. It's his assault rifle that gives him confidence he'll have a shot at survival.