What I said is exactly what I meant, meaning the base diameter. I can't find a nominal base diameter for .32 Long Colt in any of my manuals (they only date to mid-1950s), but the cartridges I have measure .313-.316. .32 S&WL base dia. is .337, a difference of ca. .021. .32-20 base dia. is .353, only .016 larger at the base than .32 S&WL. The .32-20 neck is only slightly larger than the .32 Long Colt case, ca. .322, about .015 smaller than .32 S&WL. In other words, there is roughly .006 more difference between .32 LC and .32 S&WL than between .32 S&WL and .32-20. What makes .32-20 a bottle-neck cartridge is difference between the the smaller neck and the slightly larger base, not the larger base! Don't argue unless you are prepared to learn.

To add to the question, .32 ACP can be shot in a .32-20 too! True, it won't headspace on the rim which is approximately the same diameter as the .32-20 base, but if you cock the gun while pointed up and lower the muzzle carefully they will fire. One of the gun-rag wags wrote this once years ago and I just had to know. Before anyone starts to say it won't work, it does! Definitely only something to be done if absolutely necessary, but it will work and is safe with a low pressure cartridge.