There's really no set rule, for how much brass I keep on hand for a particular cartridge (or firearm). I generally just keep adding to the supply, until I get to a point that feels "good enough".
For the .327, that point came when another .327 shooter dropped me a line on some once-fired stuff (last year?). I had 250-300 cases on hand (some still factory loaded), and added 500 once-fired nickel. Shortly thereafter, my order of 500 .32 H&R cases arrived. I already had 200-300 .32 S&W Long cases, 100 .32 S&W cases, and about 50 .32 Auto cases. In total, I had 1,600+ pieces of brass for a single revolver. It was actually more
than I considered "good enough".
...But Crankylove helped me remedy that situation, when he bought a .327 SP101. I gave him a few hundred .327 and .32 H&R cases.
In contrast, my other (Super) Blackhawk, only has a brass count of about 350 pieces. And, that includes 50-75 .44 Special cases. Right now, only 75 cases are available for loading; and it doesn't bother me one bit.
I'm really hurting for 9mm, though. I only have about 4,500 processed cases, and 1,800 unprocessed cases on hand. It'll be a while before I need them, though. I loaded a substantial quantity over the winter.