iraiam For example 380 acp does not measure 380, nothing about it does. Its only a thousands but that also the difference betwen a many others. The 357 sig is not made from 40sw brass ether and as others noted it does not use a .357 bullet. Same .355 as a 9mm but even then with some bullet makers they do list a heavier jacket on the bullet for the "sig cartidge too.
Yep I did get my numbers mixed up, I was thinking 38 auto not 380 auto I think the actual spec may be .384 (38 auto) and not .380, see how easy it is to get confused with this stuff, thanks for the correction.
I did not say that 357 SIG was made from 40 S&W brass, I said it was "Basically a 40 caliber pistol case necked down to .357", I admit that the .357 was incorrect, and I appreciate the correction. 40 caliber does not mean 40 S&W it means 40 caliber.
I use the term "caliber" in the way it is actually defined. A bullet that measures .357 is a 35 caliber bullet, bullets that measure .308; 30 cal, 310 31cal 311; 31 cal, 312; 31 cal I guess I'm old, sorry for the confusion.