30 poppa(30 Popper) or simply 30 is any firearm that's easily concealable with a 30 round magazine. The slang 30 is heavily used in Chicago and has gained popularity due to the rise of Drill music coming from Chicago. Rappers, whom tend to be gang associated, can often be heard referring to their weapons as 30s in their songs. Another name to describe a 30 poppa is 'mop'.
In Fredo Santa's "On That" song, he says "Got big 30's with big beams , trust me you don't want that". In Chief Keef's In This B*tch(Remix), Lil Reese says "I just hit anotha lick - Stained his ass cause he a vic - Hollow tips all in my gun - 30 poppa for the clips". In Lil Mister's Get Banged, he says "If you with the opps, you can get banged - A new 40 with a 30 you can get banged".