In this case, the reason to not "just shoot .327 Fed Mag" is because the firearm is a Ruger Blackhawk chambered in .32 H&R Magnum, made before .327 existed.
Those who reload and know this format know that there is a progression of straight wall brass made for increasingly powerful cartridges. This is rather similar to .38 Special and .357 Magnum, only more comically so.
32 S&W was made a hair longer to 32 S&W Long which was lengthened to 32 H&R Magnum which was lengthened to .327 Federal Magnum. You can also shoot .32 acp in the same cylinder as its shorter than any of the previous.
In the past, people shot very very high pressure wildcat hotrod loads in the .32 H&R Magnum chambered Single Six. Some problems with mechanical strength were observed where the even number of chambers were too close to the notches for the latching bolt.
That's why the .327 Fed Mag small single action revolver was made a 7 shot revolver and called the Single Seven- to offset the chamber and the notch for the latch.
Ruger also chambered a rare few Blackhawks for .32 H&R Magnum. In terms of strength, these revolvers are much much stronger than any small frame Single Six. The thickness of the cylinder wall in any direction far exceeds the Single 7. Don't take my word for it, measure!
One could take the .32 H&R Magnum .32 H&R magnum to a gunsmith and have the chambers bored 1/8" deeper. These cylinders can handle the length easily. While there, the throats could be measure and honed and all that fancy stuff. It just costs money and time.
In terms of reloading.. the cartridge does not care how long it is, since it head spaces from the rim.
The ignition does not care how long the brass is. The ignition cares about how much volume there is to put the powder in, and the tension on the bullet at the time of ignition.
So long as the internal volume is the same, and the bullet has a good crimp and as well the bullet is not seated against the forcing cone, extra brass length is not relevant.
Okay. But those of us that have shot this stuff mostly have the same impression for the VERY high pressure .327 Fed Mag. Even hot loaded wildcat loads between 32 H&R and .327... Wow are they loud. In a very light handgun, people say "wow, that stings my hand!"
Many of us are delighted by a 100 grain (or maybe a 115 Lyman) cast bullet going about 800 feet per second. Nothing close to 1200 fps or more.
This is not a deer hunting round for revolvers and should not be used for that.
A milder load will wallop pest animals, tin cans and pine cones. No one is volunteering to stand in front of even a ".32 Long" level projectile. They're not paintballs, they will kill ya.
If I were to get a new .32, it would be the Single Seven. One never needs worry or think much about the reloading. So long as the pressure from the recipe is less than .327 Fed Mag maximum, it's not too likely your gun will blow up.
I would not care for a Blackhawk in .32 because they are great big heavy revolvers and it's like shooting .410 shotgun loads out of a battle tank.
When we understand the science behind what is going on, we get beyond "Follow recipe safe, not follow recipe disaster" thinking. We get to "this is my gun, my load. I studied this and it's MY CHOICE. Don't follow me blindly, we're just discussing our experiences."
. Found good loads for 'my' guns with that powder. Plus it meters well into the small case. I personally think it is more 'suitable' for the cartridge than H-110 or Lil Gun, but that's just my feeling.