Nelly -- Busted for Pot & Meth ... Cops Say Guns Also On Tour Bus

Nelly's tour bus got nailed by cops in Tennessee for a bunch of alleged offenses -- and the rapper himself got hauled off to jail for felony possession of drugs ... including meth.

A state trooper pulled over the bus Saturday morning for not having a required Dept. of Transportation sticker ... and when the officer caught a strong whiff of pot ... he decided to conduct a search.

Cops say they found a baggie with crystal rocks that tested positive for meth, and a small amount of marijuana in the sleeper area of the bus. They say they also found quite the stash of guns -- a .50 caliber pistol, a .45 caliber pistol, and a .500 magnum Smith and Wesson.

Nelly was booked for the meth -- a felony -- and misdemeanor marijuana possession. He was also booked for drug paraphernalia -- cops say there were about 100 small Ziplock bags commonly used for the sale of drugs.

Another passenger, Brian Jones, was busted for possession of a handgun.