One expert said the weapons, which were believed to include assault rifles, handguns and stacks of ammunition, were likely to be connected to terrorist activities, although police, who said it was a "significant find", would not be drawn on their investigation.
More than 20 officers, including forensic teams, swooped on a property in Killermont, near Bearsden, East Dunbartonshire, and scoured nearby woodlands after a call from a member of the public at 6.30pm on Thursday.
They removed the weapons in bags and boxes to be taken away for testing, and cordoned off the area.
Last night the businessman who found the haul of guns worth thousands of pounds described them as "enough to wipe out a shopping centre".
Jeff Kearns noticed the bag of weapons when he was in the stables of the East Dunbartonshire farmhouse he rents with four other men.
The 40-year-old claimed he found them stuffed into a black canvas bag in a bin outside Kessington Farmhouse, set within an old dairy farm on the fringes of a residential area.
Mr Kearns, who owns a shoe repair and key cutting business, said he found "a lot of guns" when he unzipped the bag.
He added: "It was enough to wipe out a shopping centre, put it that way. There was a British Army rifle SA80, two handguns, two AK47s, a shotgun and tons of magazines (ammunition storage devices).
"I found them in a black canvas bag in a round bin beside the house. I had no idea what it was to start with, but when I opened up it all started unravelling. I called the police and they came to inspect the guns. After that they started searching around the farmhouse."
Mr Kearns said he did not know how the firearms ended up outside his home, which is near Boclair Academy.
He said: "I have no idea who put them there, none at all. It's a mystery to me."
Nicknamed "Heartbreak House", the farmhouse is thought to be rented out to men who have split from their partners, and may also be being used as a music studio.
Mr Kearns and his housemates were yesterday helping the police with their inquiries.
Residents living on the quiet residential streets nearby spoke of their shock at the haul.
Christopher McFarlane, 20, who lives on Woodvale Avenue, said: "I came back to my house at about 10pm.
"There were about 10 police cars parked outside my house and there was loads of activity going on at the farmhouse.
"Nothing like this ever happens here, it's a quiet place."
LibDem councillor Ashay Ghai said: "Obviously such a discovery of heavy-duty weapons is of huge concern to me as a local representative.
"The farm has been a natural landmark in the area for many decades and a working dairy farm until only recently.
"It lies on the doorstep of the local secondary school, many walk their dogs a stone's throw away from the farmhouse and parents often take their children to feed the horses in the adjacent field."
Officers from the Serious Organised Crime Agency (SOCA) spent several hours yesterday examining the farm.
Earlier, Det Supt Downie said the investigation was focused on finding how long the guns had been there. He appealed for anyone with information to come forward.
He said: "Whilst we cannot confirm the types of firearms found, this was a significant find. Our enquiries are at an early stage and police are still at the scene carrying out inquiries."
Security expert Professor David Capitanchik, retired professor of terrorism studies at Robert Gordon University, said he believed the cache would be connected to terrorist activities. He said: "My feeling is that this material in some way is related to some form of terrorist organisaton, whether it is currently active and training, like al Qaeda, or if it is related to previous activity connected to Ireland.
"Scotland of course was well known as a place where guns and ammunition were kept during the unrest in Ireland.
"What we don't know is whether these weapons have been there the whole time or whether they have been brought here recently for a particular purpose.
"The only other possibility is that these guns are to be used for some sort of criminal activity."