Sizing heavy gent’s rings can be difficult because of the metal thickness in the shank. Straightening the ring on a ring mandrel can be particularly challenging. Using a Lead-filled weighted rawhide mallet, or a dead-blow mallet will provide the extra force needed to make this job easier.
In addition, when opening-up a shank for up sizing, one of these mallets can be used to force the ring down on a ring mandrel, after sawing through the shank.
~Unknown Jeweler

