.32 S&W Long will not chamber in a revolver chambered for .32 S&W due to the length difference. As stated, .32 ACP will fit and fire in a .32 S&W chamber, but as its chamber pressure is much higher, it is not safe to do so in any of the old top-breaks. I have done it with no problem in later solid-frame revolvers chambered in .32 Long. .32 S&W is difficult to find, even though it is still manufactured - or at least I think it is. A gun shop might special-order it for you if you are willing to pay the price. .32 S&W factory ammo loaded with smokeless powder is perfectly safe to use in older BP-era guns. It is loaded lightly, to pressure levels and velocities about the same as the old BP loads. The same is true for the ammunition made in most of the other older calibers from the BP era, such as the .38 S&W.