I turn and chamber all my own barrels and polish the chambers after reaming to #320-#400 and ensure there are no marks in there
I have no experience with chamber fluting, but a good chamber shouldn't be necessary. That said though, it's pretty hot where you are, esp Victoria, so that may be a factor
One thing though, why .308 and not just .223? The smaller cartridge has many benefits over .3908 in a SP and is more than capable