Machine Gun Kelly Disses Jack Harlow in New Freestyle Rap

Machine Gun Kelly has entered the chat for the "second greatest white rapper" debate after Jack Harlow declared himself heir apparent behind Eminem ... and he might have a claim.

MGK -- who's been much more about rock and roll lately than he has about rap -- just dipped his toe back into the genre where he cut his teeth ... dropping a new freestyle in which he's spittin' pretty ferociously, and where he also takes an explicit shot at Jack.

Check it out for yourself ... Kelly is rapping over Jay-Z's "Renegade" beat, which also features Em -- something that surely wasn't lost on MGK when he was picking an instrumental.

As for the bars themselves ... we gotta say, they're pretty damn good. Solid flow and rhyme scheme -- and the references he's making are a cut above your average mumble rap verse these days. Of course, he eventually called out Jack by name with a telling few lines.

Kelly raps, "Make sure there's no confusion // I'm a great white, I can eat these barracudas." Then, he goes for the jugular ... "I see why they call you Jackman // You jack man's whole swag // Give Drake his flow back man." Indeed, it's pretty vicious, and there's no ambiguity.

This is clearly in response to what Jack said on one of his tracks from his new album -- in which JH rapped ... "The hardest white boy since the one who rapped about vomit and sweaters // And hold the comments 'cause I promise you I'm honestly better // Than whoever came to your head right then." That claim caused a firestorm on Twitter.

Other names got thrown around as possibly being better than Jack ... including the underrated Action Bronson, Lil Dicky, Mac Miller and, yes, Machine Gun Kelly too.