Junior says that the department's new bullet-proof vests will withstand a ".357 Magnum .50 caliber." This is an oxymoron: a .357 Magnum and a .50 caliber are two different rounds. It is either a .357 or a .50 caliber, not both.
This is not a goof. The gang of Reno 911 is very ignorant of all things weapon related. This is an intentional joke.