Every time I think about fixing a too-wide barrel/cylinder gap I remember the section of Hamilton Bowen's book "The Custom Revolver" where he describes the procedure of setting a barrel back to correct the gap, and notes that it essentially is the same as installing a new barrel. So, if you need to set a barrel back, it might be best to just get a new barrel while you're at it unless your current barrel has markings or features that cannot easily be replicated.