The weapons assembled here flowed into the city through the same “Iron Pipeline” that supplied the Glock handgun used to kill NYPD Officer Randolph Holder, authorities said yesterday.

The weapons are among 74 firearms — including pistols, revolvers, rifles and at least one sawed-off shotgun — that a gang of traffickers allegedly smuggled up from South Carolina and peddled to undercover NYPD cops during a nearly yearlong sting operation.

Two of the illicit gun sales took place on East 102nd Street in East Harlem — the same street where last week, a drug-war gun battle erupted, leading to Holder’s murder.

The weapon that killed Holder was purchased by Roderick Hughes from a store in Columbia, SC, Lawmen’s Safety Supply, law-enforcement sources told The Post.

It was reported stolen from a law-enforcement officer in Marion, SC, in 2011.

That officer is unnamed in records, but Hughes, 39, is a state trooper.

Local cops were told at the time that the .40-caliber Glock was taken from a car.

A New York gun-gang bust on Tuesday netted six suspects, including a former Marine, just hours ahead of Holder’s wake and exactly a week to the day after he became the fourth NYPD cop shot dead in less than a year.

The ring’s alleged leader, Samuel “Scrappy” Barreto, had posed in a photo posted on Instagram flashing gang signs with his middle fingers extended — while standing on the hood of an NYPD cruiser.

During a news conference announcing the arrests, top cop Bill Bratton ripped Congress for not doing enough to help stem the flow of guns from the South.

“We have a spigot that’s wide open down there, and we don’t have a national or local ability to shut that spigot down at the moment,” the commissioner said.

“It still amazes me, the insanity of the United States Congress, that they just don’t get it. And I don’t know why they don’t get it, other than that they basically are constantly down there with their hands out to the NRA, looking for more and more money, and it’s just insanity.”

Holder’s accused killer, Tyrone Howard, was indicted Tuesday.

Manhattan District Attorney Cyrus Vance Jr. said the suspects charged in the gun bust Tuesday conducted their illegal business brazenly, noting that “each of the buys took place in residential neighborhoods in broad daylight.”

The final two transactions of the undercover operation took place on East 102nd Street, with the first occurring on July 22, when Barreto arranged to meet an undercover cop, court rec­ords show.

When Barreto showed up with an unidentified accomplice, the cop allegedly handed over $1,400 in exchange for a Romarm Cugir 39mm semiautomatic rifle.

Baretto was ordered held without bail during his arraignment in Manhattan.

It was revealed that one co-defendant, Michael Rivera, is a former Marine.

Additional reporting by ­Jamie Schram, Ben Feuerherd, Daniel Prendergastand Bruce Golding