Small Base Dies

DaveB · Nov 12, 2014

I never paid any attention to SB dies. I had regular FL and a few neck size dies and they worked as intended. Besides, I understood SB dies were intended to bring machine-gun fired Brass back into spec's for use in Bolt action guns with chambers that meet SAMMI spec's. Lots of 223 and 308 brass Lake City in particular will not chamber even after being full length sized. Tight is an understatement.

So then I read in the Midsouth web site that SB dies for the 300 WSM caliber are only for non-bolt-action rifles. HUH? What is this?

Any one have knowledge why the SB thinking is backwards/different for this caliber?

Hunter 257W · Nov 12, 2014

I've always thought of them being for any semi-auto rifle regardless of the specific cartridge. Bolt actions have an advantage with chambering that semi-autos don't. Plus supposedly some semi-autos have slightly larger chambers and bulge cases more. Since I've never had, nor intend to have, a semi-auto rifle that I reload for, I have no actually experience with the SB dies.

Rubberduck270 · Nov 12, 2014

DaveB said:
I understood SB dies were intended to bring machine-gun fired Brass back into spec's for use in Bolt action guns with chambers that meet SAMMI spec's.

Um, no.

Small base dies size brass down below (smaller than) SAAMI spec to insure they'll load and extract from semi-autos. Both bolt guns, semi-autos and whatever gun you have is supposed to have a SAAMI spec chamber (excluding wildcats of course). That's why there are detailed specifications for each cartridge. The problem with semi-autos is the bolt has no mechanical leverage (i.e. the bolt handle) to force a cartridge in and out of the chamber. Small base dies underdersize the brass so they fit loosely in the chamber, easing their loading and extraction.

Generally you don't want to use small base dies for a bolt gun because it'll overwork the brass on each firing, giving you significantly shorter brass life. And not all semi-autos have to have small base dies, just ones that have problems feeding FL sized brass.

mr.big · Nov 12, 2014

I am gonna guess and say some WSM factory ammo is loaded really hot to get the FPS up to meet the claims of the Short Magnum craze,,fired in some rifles the brass from this factory ammo may need a SB die to chamber after being reloaded,,just a theory

Tiny · Nov 13, 2014

It isn't just semi auto or WSM.. We've generally always use the Small Base for any auto an at least the first time on range pick up brass were we can meaning we have that caliber on hand.
They can make sure that range pick up will fit any rifle we run em in. The first time after that regular Full Length Sizers work fine,may have to fine here an there as I had to for my 300WSM an a couple 3006 after getting set for the tight one left the sized set so any case will run in the other.