The haul, found in a cellar in Spånga and an apartment in Sundbyberg, included grenades, antitank grenade launchers, automatic weapons, pistols and explosives.
The swoop took place in July and the suspects were arrested between end of July and August.
The weapons are both military and civilian, some of which have been stolen in Sweden, others from the former Yugoslavia.
Ulf Göranzon, a press spokesman at Stockholm police, described the weapons as being “generally very heavy”.
Speaking to the TT news agency, Göranzon said it was “worrying that it is so easy to procure weapons from that part of Europe. There are plenty of weapons in those countries.”
Prosecutor Henrik Söderman is also concerned by the extent of the weapons seizure. He has requested a fresh hearing on the detention issue on Friday.
“Of course one is a bit jumpy,” Söderman told TT. “We are talking about weapons such as antitank grenade launchers and and explosives”.
Söderman could not comment on whether the weapons were meant to be sold or used in robberies.
The six suspects are all aged between 22 and 27 and are already known to the police. A few of them are suspected of serious weapon crimes, and one is suspected of smuggling. All the men are from the Spånga and Järfälla suburbs in northwest Stockholm.