View Full Version : RCBS X-dies small base - why?

July 23, 2007, 00:49
Just curious as I'm going to be buying .223 RCBS X dies soon and would like to know what a small base die gets me.

July 23, 2007, 00:56
A slightly smaller diameter base which ensures reliable feeding in semi-autos. Or so they say. I've had no problems using regular dies for 223, 7x57, 308, and 30-06 for semis.

Downside is that they work the brass more and that shortens case life.


July 23, 2007, 02:00
I've been told the SB dies are useful for resizing machine gun fired brass.

I too use only standard dies and have never had a problem.

July 23, 2007, 10:29
RCBS "X" dies and small base dies are two different things.

The small base sizing die has been explained above.

The RCBS X die is machined so that it keeps the overall length of the resized case from growning longer during the resize operation. It requires the brass be trimmed to a uniform length before sizing. From then on, the X die keeps the brass from growing during the reloading operation.

I haven't tried one yet. I don't know how it works.

English Mike
July 23, 2007, 11:04
.223 RCBS X dies are available in both standard (#37212) & small base (#38862) versions.

I found this out yesterday, as I nearly put the wrong ones on my shopping list.


July 24, 2007, 14:19
What's the chamber 'size' in the firearm you are reloading for?
Is it bolt action or semi auto?

If you are loading for a semi auto firearm with a Win 223 chamber, then you may need the small base dies for reliable feeding.

If you are loading for any other combination (semi+5.56 NATO chamber, bolt+Win 223 chamber or bolt+5.56 NATO chamber) then standard dies will work for you.


July 24, 2007, 23:46
Originally posted by ENGLISH MIKE
.223 RCBS X dies are available in both standard (#37212) & small base (#38862) versions.

I found this out yesterday, as I nearly put the wrong ones on my shopping list.


Exactly my point, Midway lists both, and I wanted to know which to get for AR blasting ammo and AR Match ammo. SteveW, don't own a bolt gun in .223. Yet... Looks like small base dies for me.

What did you go with Mike???

English Mike
July 25, 2007, 14:23
Standard base, as they will be used to feed a bolt action, rather than a semi.

July 25, 2007, 20:53
"SteveW, don't own a bolt gun in .223. Yet... Looks like small base dies for me."

Okay, but is your semi auto chambered for .223 rather than 5.56 ?
It should be stamped on the barrel.
If it's an AR they are pretty well all chambered for 5.56.

Even if you have an 5.56 chamber, then a small base die won't 'hurt', but it will work the brass some. You might get fewer loadings from your brass.. If you care...


July 28, 2007, 00:24
Steve, Armalite & Colt ARs right now, 5.56s, and if/when I get a bolt gun I'll just neck size.

I may be loading for a National Match upper, though, so I'm thinking I might actually get two, small base for match ammo (whose brass will get worked a bit more) and a regular base for blasting ammo.

Sound right?

July 28, 2007, 10:53
I guess. I am from a different school of thought on loading target ammo.
IMHO, the more you work brass (during the resizing process) the less accurate the resulting round is. I am looking for target ammo that when loaded holds the bullet as concentric to the bore as possible. I also prefer the loaded round to fit the chamber as closely as possible.

I have measured the headspace length on my ejected brass.
When I am reloading it, I neck size (Lee collet die) then body size (Redding body die) the brass to 0.004" less than the size of the ejected brass (using the same tools to measure). All in a progressive press..

Like I said, I would rather have the brass fit the chamber as closely as possible, but still reliably chamber the round. The 4 thou difference gives me that.

I get a 0.002" to 0.003" bullet run-out in that way, regardless of if I am loading plinking or target ammo. The difference to me is that target brass gets a lot more attention (primer chamber reaming, deburring flash holes, weighing, cleaning out the mouth, etc..etc..)

I am loading for just the one semi auto in 5.56, but the headspace measurement after reloading is such that it will work in any gun as it is below maximum specification. I load both plinkers (55 gr) and target ammo (52/68 gr) the same way. The difference is the case prep and the bullet.

Agreed, neck size only for the bolt, but personally I would just bump the shoulder back by a thou at each reloading.


[edited for spelling and clarity]

July 31, 2007, 00:15
Good post. I just figured that the small base dies might be needed to resize to a tighter match chamber. But, it would seem that that is not the case (pardon the pun).

I suspect that I will buy a separate set of dies for match loading, and I hadn't considered what you're describing with your multiple die setup. Sounds interesting.

In the meantime, I'll be ordering a set of X-dies, and I think I'll go for the small base just because I may be reloading cases fired in an M-249 at some point. I've got a set of Hornady New Dimension dies for my "standard" .223 dies at the moment.