You should use the proper sized caul to install the felt, thereby
giving the appropriate compression set.

Bill Spurlock sells mortise sizing cauls for use in bushing work.
Check out his whole bushing system at http://spurlocktools.com.  He
also has the definitive answer to upright damper work.
  [ Spurlock Specialty Tools is closed for vacation until Oct. 31.
  [ Relief Editor.

Pianotek sells the Key Bushing Iron, an invaluable tool for sizing
installed bushings.

Jon Page