While I'm sure hydraulic COULD be made to work, and might well be the way to go were one to found the Acme Scabbard Repair Works (not to be confused with OALW) but, I think we are looking for something a bit more "primitive" - I know I am!   :-)

I have only one scabbard to do - unfortunately it's an 1894 "keystone", so I need to be VERY careful with it, especially as regards the throat area.