Matthew Groves wrote: 

"Is it possible that the entire body is actually shrinking which would
lead to a binding iron." 

Spot on!  It's exactly that the whole piece of wood, the body, is
shrinking.

"The solution remains the same regardless. grinding the iron." 

Nope.  You can carefully open the opening as well.  It's usually only a
bit too narrow and removing 1/32 from each side should do the trick,
without substantially weakening the cheeks.  It is also possible to plug
the mouth with putty and pour in a 50/50 solution of linseed oil and
turpentine which will swell the wood back to its original dimensions. 

Mike in Woodland