Why are .38 Special and .380 ACP called that when they are actually .355-358?
Early cartridges used an outside lubricated "heel" type bullet, similar to the one the .22rimfires still use today. The full diameter of the bullet was the same as the outside diameter of the case. .38s were actually .38s, .44s were .44s etc.
When the inside lubricated bullet was developed, the heel type was replaced by them, except for .22s. Now, the max diameter of the bullet had to fit inside the case. .38s became .36s (.358) and the .44s became .43s (.429) etc. For a while, the bore sizes were kept the same, as the soft lead bullets would upset and fill the bores, giving tolerable accuracy. Eventually the bore sizes were reduced to match the bullets better, but the names were kept the same.
The .38 Special and the .380acp are 38s because we were used to calling guns with those bore sizes ".38s", and those names were chosen for marketing purposes.