.32 ACP is like other auto cartridges, the rim is recessed.
.32 S&W has a rim.
You'll end up with light strikes as the cartridge moves forward, or problems ejecting the empties, or both.
I believe the .32 ACP pressure is higher than the old .32 S&W, which, I think, is a black powder cartridge. That would be really bad for your gun.
I'm going off memory here, but I really would not shoot .32 ACP in your H&R.
I would not. Saami pressure for a .32 acp is probably around 20,000. .32 S+W is about 14,000. Might shoot okay but probably more stress than the revolver was designed for.
I would not shoot 32acp in a .32 S+W long, as the overall length is shorter and the bullet has a bit of travel before reaching the rifling. It would not be accurate at all. And the case pressure issue.
32 S&W cartridge (1878-Present, Union Metallic Cartridge Co.)
Smith & Wesson K32 Masterpiece Double Action Revolver
.32 S&W Long (1896â€”Present, S&W)
Smith & Wesson 32 Regulation Police
.32 ACP (1899-Present, John Browning)
The .32 S&W Long cartridge is derived from the .32 S&W, by increasing the overall brass case length, to hold more powder. Since the .32 S&W headspaces on the rim and shares the rim dimensions and case and bullet diameters of the longer .32 S&W Long, .32 S&W cartridges may be fired in arms chambered for these longer cartridges.
.32 ACP and .32 S&W are not the same cartridge and are not interchangeable. The .32 ACP (AKA 7.65 Browning) is a semi-rimmed cartridge for autoloading pistols, .32 S&W is a rimmed revolver cartridge.
I have one of those Harrington and Richardson .32 S&W revolvers. It is a family heirloom I inherited I think it was my grandfather's. It is remarkably small. The one I have is a top-break barrel, 5-shot design that is automatic ejecting: when you open the barrel it extracts all the empty shell cases. Mine was built between 1895 and 1904 though I have not checked for serial number.
This is a lighter hitting bullet when compared to a .380 and light by today's standards but is very low recoil and mine is accurate at shot distances. I sure would not want to be hit by one.
Many 32-cal revolvers will fire 32 Automatic ammunition. I know mostly of 32 H&R Magnum revolvers, but some 327 Federal and 32 S&W Long revolvers will also fire 32 Auto. The 32 Auto is a semi-rimmed case, so depending upon the exact dimensions of your cylinder, they may hang on and fire just fine. My own 32-cal revolver (a 327 Federal) will only fire 32 Auto cartridges a portion of the time, and some of those are light-strike, squib-like firings, so I don't try that any more.
As to pressure, SAAMI MAP for the 32 Automatic is 20,500 psi via piezo transducer (15,000 CUP via the old copper crushers). The SAAMI MAP for the 32 S&W is 17,000 psi, and the 32 S&W Long is 15,000 psi via transducer (both are 12,000 CUP via the old crusher method). 32 Auto cartridges are therefore not quite as high pressure as 32 S&W proof loads, but they're much of the way there. So, personally I would NOT make it a habit to fire 32 Automatic cartridges in a revolver labeled only for one of the 32 S&W cartridges. Between the higher pressure and the possibility that the S&W-labeled gun is older or otherwise metallurgically uncertain, I wouldn't take the chance and I'd recommend others don't, either, for their own safety, the safety of those around them, and the safety of their gun.
As said, many 32 caliber revolvers can actually chamber and fire 32 Auto, but it's not a good idea, especially in an unknown old gun designed for 32 S&W.
I've shot 32 Auto in my 327 Magnums, but more as a proof of concept than anything.
Stick with 32 S&W. It's out there and available. It's not one of my favorite cartridge, especially when it comes to handloading(I'll do 32 S&W long if forced, but not 32 S&W) but it will shoot in that gun. Most that you find out there is loaded pretty wimpy in deference to the fact that most guns chambered for it are old, weak top breaks. I do keep some around especially since in a gun like my Ruger Single 7, it's like shooting a BB gun.