Keith Richards -- Rich Maniac Allegedly Made Bomb for Rolling Stones Guitarist

Well this is nuts ... a wealthy Connecticut man (who allegedly stocked hundreds of guns in his million-dollar mansion) was arrested after telling police he was building a bomb ... for Rolling Stones guitarist Keith Richards.

It's actually hilarious ... law enforcement sources tell us, 69-year-old Joseph Callahan called police last week, claiming someone had broken into his home.

When police searched the place, we're told they found a terrifying arsenal of guns and explosives, including roughly 100 pounds of ammonium nitrate (the same chemical used in the 1993 World Trade Center bombing). Short story: Callahan called the cops on himself.

Callahan told police he planned to give the bomb to Keith Richards, but had no intention of harming him.

Callahan was taken into custody and placed on a 72-hour psychiatric hold. He has been charged with 112 counts of illegal possession of explosives, reckless endangerment, and manufacture of bombs (which Callahan called a hobby).

But here's the scary part ... his lawyer tells us, Callahan was mentally unstable at the time of his arrest, but has since stabilized and been released from custody on his own recognizance.