Undersize Lee Collet Die Mandrel

Be careful buying undersize Lee collet die mandrels. I bought one over a month ago, recently went to use it for the first time. When i installed it I noticed it sat a bit deeper in the collar than my normal size mandrel. While reloading I noticed a previously FL sized case had a dented the case mouth so I tried to straighten it out with the collet die, I lowered the ram and the case pulled the undersized mandrel out with it. The rim at the top of the mandrel seems to be smaller than my other mandrels. Something to be wary of.