Some articles which discuss reloading for the .32 H&R Magnum emphasize attaining the highest possible velocity and energy, but this defeats the purpose of this mild, efficient dual-purpose, revolver or rifle small game cartridge. In my experience high velocity, JHP varmint bullets, such as the 85-gr. Hornady XTP cause excessive meat damage to table game. Higher velocities also cause more rapid bullet expansion, which reduces penetration needed for killing effectiveness on larger predator animals.
Revolver loads at around 1000 f.p.s. give reasonable trajectory to enable 100 yard hits.A 115-120 grain solid lead flat-nosed bullet such as the Saeco #322, Lyman #311008 or NEI #82 plainbase, at subsonic velocity is non-destructive for edible small game but have fully adequate energy and penetration to be effective against predators such as feral dogs or coyotes. When the same mild loads are fired from rifles velocities approach 1300 f.p.s., approximating the .32-20, adequate for some expansion with soft alloys of 8-11 BHN, giving good game performance and acceptable field accuracy with an economical, plain-based cast bullet.
Non-casters can buy and reload the Hornady the 90-gr. SWC or 94-gr. Meister .312" LFN. These lighter bullets work best with mild loads in the H&R Magnum with 3.0 to 3.5 grains of Bullseye or 3.5 or 4 grains of Unique or SR-7625, which remain subsonic in a 4-5/8 inch revolver. If you want a larger meplat on your bullets to better let the air out of bunny wabbits use the 98-gr. Saeco #325 semi wad-cutter with these charges. I normally expect 2-inch groups at 25 yards hand-held off sandbags with the Ruger Single Six and my Marlin 1894CB give the same results with iron sights out at 50 yards.
The 1894 Marlin cowboy rifle doesn't feed .32 S&W Longs unless bullets are seated out to provide an overall cartridge length greater than 1.3”. The traditional flat-nosed 122-gr. Saeco #322 cowboy bullet seated out in .32 S&W Long cases, crimped in the lubricating groove at 1.35" OAL is also suitable for the S&W Models 30 and 31 revolvers using 2 grains of Bullseye for 850 f.p.s. from the Marlin or 750 f.p.s. in the Single-Six. If you want a bit flatter trajectory and better reach at the expense of a more noise, you can increase the charge in the Ruger revolver or Marlin up to 2.5 grs. of in .32 S&W Long brass Bullseye for 820 f.p.s. from the revolver or 1030 f.p.s. in the Marlin rifle, which is very low noise.
I have not fooled much with slower powders, because it requires heavier charges of more expensive powder for not much more velocity, and these loads are much louder and less accurate than my milder loads with Bullseye.
The Lyman handbook nonsense which suggests sizing cast bullets to barrel groove diameter still persists in common folklore circulated for the .32 H&R Magnum. The usually-recommended .312 bullet diameter severely limits its potential accuracy for some users.
Cast bullets intended for revolvers should always be sized so they may be pushed through the chamber from the rear and out the front of the cylinder throat with slight resistance using only hand pressure. Cylinder throats of Ruger revolvers vary from .309” up to .314,” depending upon when the gun was made. If bullets fall through the chambers of their own weight you may as well throw rocks. If you can’t push bullets through by hand, but rounds chamber and extract freely, you can shoot them in below-maximum loads, at some expense to accuracy.
In my experience Marlin chambers run sloppy. My rifle readily chambers and extracts accepts ammunition assembled with un-sized .315 diameter bullets in Starline cases. It likes best the NEI #82 115-gr. FN (shortened version with GC shank removed, which resembles Lyman #3118) cast 10-12 BHN with 3.0 grs. of Bullseye in Starline .32 H&R Mag. cases at 1.45" OAL, using a light film of Lee Liquid Alox.
For general purpose use in modern .32 S&W Long revolvers, the Marlin 1894CB and my single-shot H&R I have settled on the 115-gr. version of the NEI #82, which is plain based with the GC heel removed. It resembles the old #3118 being .63 long with .315 bands, .303 bore riding nose and .195 diameter meplat. I cast these 10BHN from soft scrap lead, tumble in Lee Liquid Alox and load unsized at .315 in .32 S&W Long cases using Federal 200 primers and 2.5 grains of Alliant Bullseye at 1.32" OAL.
Velocity is 750 f.p.s. in my 3-inch S&W M31, 830 fps in the 4" M31 and Colt Police Positive, 870 fps in the 4-5/8 inch Ruger Single Six and about 1000 fps from the 20 inch Marlin 1894CB. Its report when fired in a rifle is like shooting a .22 LR. Velocity standard deviations are in single-digits. This load gives inch 5-shot groups at 25 yards with peep sights in either of the rifles and "about 2 inches" +/- at 25 yards from the modern revolvers off sandbags when you can screw your eyeballs in tight enough.
For those few occasions when I want a more powerful cast bullet load I use 3.5 grs. of Bullseye in Starline .32 H&R Mag. brass which gives the 115-gr. 1030 fps from the 4-5/8" Ruger single Six, and 1280 f.p.s. from the 20 inch Marlin 1894CB. This approximates standard velocity lead .32-20 loads in performance.