.327 is more than double the pressure of .32 Mag, unnecessarily so IMO. I think had the pressures been 30 to 35k max PSI, that would have been enough, still significantly higher than .32 Mag's 21k max PSI.
.327 can be loaded down to the mid 30k PSI pressures, but the problem is the guns chambered for .327 must be built to withstand full power .327 and that's where it becomes a quagmire. Manufacturers will not make a .327 revolver that's built for an in between .32 Mag and .327 cartridge (let's call this cartridge .327 Special) because if you can chamber the .327 Magnum in a .327 Special revolver, it's unsafe and the legal beagles won't allow it for fear of lawsuits.
So, we're stuck with .32 H&R Mag revolvers that could have a bit extra oomph to them if they were made in a .327 Special version or we're stuck with larger .327 Magnum revolvers that hold less rounds.