What is "small base" referring to in .223 die sets?


April 1, 2010, 07:06 AM
I am getting ready to buy some .223 dies and some of the brands, namely the RCBS X-Dies, are available in regular or "small base". I wasn't aware that the base could be different on any given specific cartridge. Can someone enlighten me?

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April 1, 2010, 07:11 AM
If the .223 you are reloading for is a semi-auto you would probably benefit from "small base" dies.

April 1, 2010, 07:23 AM
Small base dies resize farther down the case, to the web area. Unless you are buying once-fired, machinegun fired brass, it is unlikely that you will need them.


April 1, 2010, 07:30 AM
Don't bother buying the small base dies. They size the brass down a little more than a standard FL die does. It isnt needed in most cases.

April 1, 2010, 07:52 AM
From RCBS.

The Small Base Die set is intended for use for ammunition to be used in auto, semi-auto, and lever action rifles so that the loaded round chambers and extracts easily. The Small Base Sizer Die sizes the case from the shoulder to the head of the case a couple of thousandths smaller than a Full Length Sizer Die. In certain calibers it also sets the shoulder of the case back a thousandth or two more than the Full Length Sizer Die. The Full Length Die Set or Neck Die Set is not normally recommended for ammo to be used in auto, semi-auto, or lever action rifles. The Full Length Die set is recommended for ammunition used in bolt action rifles, particularly for ammunition to be used for hunting. The Neck Die Set can also be used to produce ammunition for use in bolt action rifles. The Neck Sizer Die sizes only the neck of the case so it will hold the bullet firmly. It does not size the body of the case nor does it set the shoulder back. Neck sized cases will usually chamber for three or more firings, depending on the powder charge and chamber dimensions. However, over a period of time, a slight drag will be noticed when the bolt is locked. At this point, cases will need to be full length sized and the shoulder set back so they will chamber and extract easily.

April 1, 2010, 08:55 AM
Thanks for everyone's explanations!

April 1, 2010, 11:42 AM
Sm base dies are only needed for certain semi-auto and lever action rifles known to have tight chambers.
Browning BAR & BLR sporting rifles are one of them.

AR-15's with 5.56 NATO chambers work just peachy keen with standard sizing dies.
If you have one with a tight match chamber, you might need Sm Base dies.

Otherwise, all you are doing is working the brass more then necessary.

So far in 40+ years, I have never found them necessary for anything I have owned.


April 1, 2010, 11:47 AM
So if I were loading for a variety of AR-15's all different makes and models, it would make sense to get the small base dies?

April 1, 2010, 11:51 AM

I have used nothing but a standard set of RCBS .223 dies since 1970 to load for any number of AR's, Mini-14's, and bolt-actions.
There has been no problem with any of them.

Sized brass drops feely in & out my Wilson case guage.
How much smaller do you need?

I have used surplus GI brass shot in M-16's almost exclusively the whole time.
I have no experiance with GI brass shot in M249 machineguns.


April 1, 2010, 12:01 PM
Thanks RC,

I am using one fired PMC and other common headstamps. None are from machine guns to the best of my knowledge. It's all in really good shape. I just have many friends I load for and I wanted to make sure it would fit all their guns.

The small base thing is weird. I've only seen it on MidwayUSA's website. other sites like Graf's don't even seem to sell them. Also, while I haven't done a ton of research, I've only seen RCBS even making small base dies. Hornady and Lee don't appear to.

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