260 die for 6.5mm?

case length difference is 0.1846" between the 2. You might hit the shoulder/neck junction of the die, damaging the shoulder angle of the case before the neck gets into the collet portion. Maybe try it on an expendable piece of brass, but I don't think it would work.
 
I will watch for that. It occurs to me that the major diameter of the decapping rod might hit the case web before the collet is lowered fully onto the neck. Maybe I can have a new decapping pin made if that is the only problem.
 
Some collet dies can be used for other cases if you understand how it works .Take the collet die apart and put a case into the shell holder and put the case into the lower part of the collet and see if the shoulder hits before the shell holder .If it does and the distance isn't too much from the shell holder you can shim the top of the shell holder so it hits before the shoulder .I use a 308 collet die to size 7.62x54r brass by putting a washer on top of the shell holder .I cut a slot in it and super glued it to the shell holder . Arnie