RCBS X Die Small Base Sizer Die

I bought the set and found the instructions to be unclear. So i called RCBS and asked and what i related whas how it was explained to me.

With that said you can tune how you use the die, it gives you options. I trim to the specified trim to length in the manual. After firing i size 1 piece twice. So a full size, then back up into the die and set the mandril to that length, so it should keep the growth uniform. Accepting that i may have to trim my brass twice during its life.

But it gives you options to eliminate or reduce trimming, and im all for that.
 
How was runout? I was going to put this die in my first stage on my dillion, then use an expander mandrel on the second stage, then charge the case with powder on the third, the fourth and final stage seat the bullet.
 
I have the X die for 308 and toyed with it. Honestly, when I got the Geraud trimmer, I haven't touched it since. I have shifted to 223 for volume shooting. So, I am not shooting enough 308 for it to make a difference to me. I will by 500 new Starline 308 before worrying about trimm8ng again.
I think my experience has probably been duplicated by others.
 
So I set up The RCBS X die, these were trimmed to 2.478 (30-06) I then took a case that was trimmed to 2.484 and set the mandrel on hard stop at that length. Gave myself .006 of growth.

Now, I ran the same case in the die to set my shoulder back about 4 thousandths From about 2.035 to 2.031

The shoulder measurements came out spot on so just by pure luck I thought, I might as well check the length. To my surprise the case length shrunk from 2.478 to 2.464.

I ran a second case same exact thing happened the case overall length shrunk to 2.464

Can someone explain to me what is happening?

I dropped these in the case gauge and no issues, The brass had to flow somewhere im assuming it went outward
 
Unusual. It suggests the die is a bit wider than your other sizing die. Measure shoulder diameter and case diameter just ahead of the pressure ring out in front of the head. Die tolerances are a couple of thousandths, and fattening that much over the body length could produce shortening by lowering the neck together with the shoulder.
 
I will measure and compare the differences.

I will just go back to the dillion die and finish loading this batch.

These were also freshly annealed before sizing
 
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Unclenick said:
Unusual. It suggests the die is a bit wider than your other sizing die. Measure shoulder diameter and case diameter just ahead of the pressure ring out in front of the head. Die tolerances are a couple of thousandths, and fattening that much over the body length could produce shortening by lowering the neck together with the shoulder.
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Nick, Could I still shoot these cases in My M1?
 
It should still be good. You can check that the diameters still fall within those on the SAAMI drawing or the military drawing.
 
Small base dies are all I use on my rifle cartridges. Noticeable difference between Full Length and Small base sizing concerning cycling function in receiver.
 
Sure Shot,
I own 4 FLS dies for 30-06 none of them are small base sizing dies. I have sized thousands of 30-06 cases and never seen this happen with one of the other 3.
 
Several of you have mentioned disabling the X-die function. I have been using one for .223 but nothing is mentioned about disabling the X- feature to resize normally.

How does one do this?
 
Just back the decapper adjustment out until the case mouth stop in it does not make contact with your case mouths any longer.
 
akinswi
I'm glad you've had good luck with Full Length sizing dies. As for me? I see to it my cartridges are minimum published tolerance sized.
When I throw the bolt on my 270. I want its cartridges to load and eject as easy or easier than new store bought. You get that cartridge performance with Small Base resizing die use. Tip: any rifle cartridge that's fired in a semi automatic mode. That cartridge has a Small Base sizing die supplied by most reloading die manufactures. Sizing with a SB die use. Is a re-loading bench tweak I do.
 
Sure Shot Mc Gee said:
akinswi
I'm glad you've had good luck with Full Length sizing dies. As for me? I see to it my cartridges are minimum published tolerance sized.
When I throw the bolt on my 270. I want its cartridges to load and eject as easy or easier than new store bought. You get that cartridge performance with Small Base resizing die use. Tip: any rifle cartridge that's fired in a semi automatic mode. That cartridge has a Small Base sizing die supplied by most reloading die manufactures. Sizing with a SB die use. Is a re-loading bench tweak I do.
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RCBS does make a SB X Die for 30-06, I should have gotten that one
 
It really depends on the gun's chamber. I've run into a couple of folks with ARs that just would not feed reliably if an SB die was not used, but I haven't noticed the issue. Some of this is luck of the draw. RCBS told me in an email that they have a 0.002" tolerance on die dimensions, and it could be those folks just happened to get standard dies on the loose side. But I've never had a feed failure in my Garands or M1A using standard sizing dies.

The small base die does narrow the case more, so it is a positive for avoiding slamfires in floating firing pin gas guns. But that narrower sizing also works the brass more, so it's a negative for brass life, and, in some guns, it may be a precision negative by making bullet alignment with the throat less precise. It would have to be tested in your chamber to see about that one way or the other.

Incidentally, those separately resizing case bodies in a Redding Body Die followed by a Lee Collet Style sizing die for the neck can get the Redding dies in a small base configuration for 30-06 and 308W.
 
Amongst my collection of .223 dies I have standard RCBS, Small Base RCBS, Lee Standard dies, and Redding Body only sizing dies. Here’s the interesting part, they all size the cases to the same size at the base.
 
Despite the name, the base itself won't change because the shell holder deck height keeps the resizing portion of the die from touching it. The resizing change stops at the pressure ring, and just in front of that is where you want to measure for a difference.
 
Unclenick said:
Despite the name, the base itself won't change because the shell holder deck height keeps the resizing portion of the die from touching it. The resizing change stops at the pressure ring, and just in front of that is where you want to measure for a difference.
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This is where I did my measurements, I could have worded it better. Basically my point was due to variances in tolerances having a ‘small base die’ might not really mean anything.
 
Correct. If you have a conventional die on the small side, the tolerance range, and a small base die on the large side of it, you may get no diameter difference. Note that this assumes the setup is sizing all the way to full die contact with the shell holder deck. If you are sizing to a different resulting head-to-shoulder measurement, the lack of difference can be due to the taper of the case profile.
 
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