At a news conference in his building, U.S. Attorney Zane David Memeger said ATF agents had "purchased" the guns from the defendants in several undercover operations.
Those firearms include revolvers, semiautomatic handguns, sawed-off shotguns and rifles, and military-style semiautomatic rifles, he said, adding that some of the guns were sold with obliterated serial numbers, making them difficult to trace by law-enforcement.
Seventeen of the 22 were arrested Thursday, 15 during early-morning raids in the city by ATF agents and Philadelphia police. One surrendered outside the city, and another was arrested in South Carolina, where he lived.
The five others were already in custody. The 22 defendants range in age from 19 to 40.
The U.S. Attorney's Office released 11 indictments unsealed Thursday in the operation. Not all of the defendants' cases are connected.
Memeger said one case was so "brazen" because it involved selling guns "in broad daylight" outside the Kensington rowhouse of one defendant, Luis Ramos, 34.
According to a 45-count indictment naming eight defendants, Ramos' house on Atlantic Street near Frankford Avenue had been a hive of gun-selling activity since February 2011.
"The gun sales were so blatant, the buyer could drive up and have a gun delivered to the car," the U.S. Attorney's Office said in a news release. Ramos, who was among those arrested Thursday, is a felon who is not permitted to possess guns.
Another indictment naming four defendants alleged that illegal guns sales took place at a house on Jerome Street near 16th in Nicetown and an apartment on Frankford Avenue near Tioga Street in Kensington.
While investigations into the defendants had been under way since 2010, there was a "focused effort" beginning in June with the formation of the Violent Crime Reduction Partnership, a joint effort between the feds and local authorities to fight violent crime, Memeger said.
Contact Julie Shaw at 215-854-2592 or email@example.com, or on Twitter @julieshawphilly.