The guns often arrived by Chinatown bus, packed into patterned bags and destined for sale in a Brooklyn rap studio or in the backs of cars on the Lower East Side.

Many had been stolen by criminals in the South, and would probably have been bought by other criminals, but instead they ended up stretched across a pair of long blue banquet tables in Police Headquarters on Monday, evidence of what officials said was the largest gun seizure in New York City history.

“A lot of firepower,” Mayor Michael R. Bloomberg mused as he paused to look at some of the 254 guns — large-caliber pistols and military-grade weapons modified to improve aim and avoid detection — that were bought by the police during the yearlong undercover investigation.

In a 264-page indictment announced on Monday, prosecutors said 19 people in two separate but loosely connected rings brought the guns to the city from North and South Carolina for one simple reason: they could buy low where regulations were loose and sell high on the city streets.