Originally Posted by
gemihur
SB dies are designed to accommodate the tolerances of semi-auto feed to chambers, and are NOT generally recommended for bolt and pump action firearm reloading.
Here's some light reading to update your own information, copied directly from RCBS's product page:
Originally Posted by rcbs product page
The Small Base Sizer Die is for bottleneck type cases used in tight-chambering semi-automatic, pump or lever-action firearms.
Here's the link:
RCBS Small Base Die Product Page
Here's more of the same from Forster on their dies:
Originally Posted by Forster reloading dies product sheet
308 Small Base retains same headspace A
as the 308 Win.; however, it reduces case body diameter B by .003" from the 308 Win. This sizing is sometimes required for the proper action of ammunition intended for use in automatic, semi- automatic, slide, pump and some lever-action rifles.
And its respective link:
Forster Products Brochure