Originally Posted by phox_mulder
They called them "Five-Sevens" a couple times, which are capable of being fired from a pistol.
(FN 5.7×28mm, most recognizable as used by Stargate SG1 in their P90's)
5.7x28 is indeed considered a pistol round. They do indeed make armor piercing bullets for the 5.7x28 and they are indeed illegal to sell this to civilians.
As Tivogurl pointed out though, what they were holding up in the show do indeed apear to be 5.56x45 rounds....they were far too large for 5.7x28.
They pointed out that the Mexicans use 5.7...which is indeed popular with Mexican drug cartels.
The only handgun I know of which shoots the 5.7x28 is the FiveSeven that you posted a picture of. The gun they showed the characters shooting however was a Heckler and Koch USP which only comes in 9mm, .40 S&W and .45 ACP.
They got some stuff right, and other stuff miserably wrong.