Q.G.
I purchased the tubes, cameras and lenses new from Calumet about 15 - 16 years ago. When the first jam occurred the camera was sent back to Hasselblad whose technician told me it had happened to him as well and they replaced a part that had been changed because of some type of a flaw in that part. Obviously others were having a similar problem or they would not retool the part. The equipment was still under warranty at the time. It has jammed once or twice since with no explanation.