No, they are not. They used the same barrels. At least those I've slugged and measured. The chamber of the .38 S&W cylinders are larger, as the OD of the cartridge cases are. Many .38 S&W chambers had the shoulders reamed, which could result in split cases. But the barrels were identical. I've swapped out quite a few cylinders for .38 Special back when they were relatively cheap.slug the bore, they are much larger than the .357 and .355 bullets readily available.
a true .38 calibre