The magazine tube on a 92 rifle is not attached to the receiver, it just sits in a hole. It is kept from moving forward by a crosspin through the magazine ring and a lip on the magazine plug fitting into a slot in the bottom of the barrel at the muzzle.
Note that if removing the magazine tube on those guns, you first remove the magazine plug (careful the spring doesn't kink), then drive out the cross pin in the magazine ring. The tube can then be pulled forward. To remove the magazine ring, use a rod the size of the magazine tube to turn it; it is curved and trying to drive it out like a dovetail will damage it and the barrel.