Cops found a .25-caliber gun on a Brooklyn man Thursday, moments after he was busted for a MetroCard scam, law enforcement sources said.

Donovan Hunter, a 27-year-old from Bedford-Stuyvesant, got a two-ride MetroCard in exchange for giving blood and then tried to sell that subway pass to undercover cops at the 28th Street station in Manhattan for $3 at 11:35 a.m., sources said.

Hunter – arrested for unauthorized sale of a fare card, a misdemeanor – was then searched by those cops, who found a loaded, .25-caliber Taurus handgun in his left coat pocket, sources said.

Hunter now faces more serious charges – for criminal possession of a weapon and criminal possession of a loaded firearm.

He’s a transit recidivist, having been pinched eight times before for turnstile jumping