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Posted: 11/19/2012 2:52:34 PM EDT
I'm just setting up my press heads for 233/556 and 308, to be used in semi-autos. If I understand correctly, a small base sizing die will size the case .003 smaller at the bottom than a full length die. Are the small base dies what I should get to facilitate  smoother loading in my ARs? Or, what is the reason for using a small base sizing die over a full length die?
Link Posted: 11/19/2012 2:58:17 PM EDT
[#1]
They essentially return the case to new dimensions.

They are not needed for reliability in semi-autos - despite many people who will claim exactly that.  In fact, the average .223 or .308 caliber semi auto closes with more than enough authority to resize even an over sized case.

What it can do for you is allow the round to sit more consistently in the chamber and it may improve accuracy in some cases, especially if you are using the rounds in more than one rifle.

Link Posted: 11/19/2012 3:01:40 PM EDT
[#2]
You'll get a thousand different views on this issue As for me, I'm sticking with the small base dies, as it would guarantee fit, and function on almost any auto loading rifle. BTW, Dillon 223 dies are small base dies.

GlockMonk
Link Posted: 11/19/2012 3:08:29 PM EDT
[#3]
Small base dies overwork your brass even worse than normal FL dies.
Link Posted: 11/19/2012 3:31:11 PM EDT
[#4]
On one toolhead (I have a Dillon 650) I was going to set it up for primary brass processing. Decap in #1, 1200 trimmer in #3 and then a sizing die with an expander ball to clean up the inside of the case mouth in #5. I wanted to use the best kind of sizing die that would be the easiest on the brass, but also give me the most reliability. I have read where some folks use a full length size/decap/expander ball in station #1 to get the case mouth round for trimming. But if the Dillon sizing die that you have to use with the trimmer is a small base die, it looks like it kind of limits options. Am I wrong on this?
Link Posted: 11/19/2012 6:24:58 PM EDT
[#5]
Use a good set of small base, it may overwork the brass a little but you gain improved reliability, plus 223 brass is cheap and readily available.  FYI - Dillon 223 dies are small base but are rarely advertised as such.
Link Posted: 11/20/2012 2:08:16 AM EDT
[#6]





Quoted:



On one toolhead (I have a Dillon 650) I was going to set it up for primary brass processing. Decap in #1, 1200 trimmer in #3 and then a sizing die with an expander ball to clean up the inside of the case mouth in #5. I wanted to use the best kind of sizing die that would be the easiest on the brass, but also give me the most reliability. I have read where some folks use a full length size/decap/expander ball in station #1 to get the case mouth round for trimming. But if the Dillon sizing die that you have to use with the trimmer is a small base die, it looks like it kind of limits options. Am I wrong on this?



To answer your question: I have a 550 and have a Forster .223 FL sizing die in station #1, Station #2 empty, Station #3 has the trimmer die and 1200 trimmer. I set the Dillon trimmer die to just hold the case enough so it doesn't spin when trimming. I don't have any desire for it to resize the case again, just trim. Station #4 has a expander die from 21st century tool (ableit a very tight fit with the trimmer). I also use the UniqueTek toolhead kit to lock the press down, an o-ring under the sizing die. I have no experience with a small base sizing die, so I can't help the OP with that. All I have ever heard was to use a FL sizing die for semi-auto. FWIW


 
Link Posted: 11/20/2012 6:18:23 AM EDT
[#7]
FL size before trimming. Look at RCBS FAQ for info on small base.
Q. I see a Small Base Die Set listed for my caliber. Do I need these or should I buy a Full Length Die Set or Neck Die Set? How does each set differ?

A. 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.
Lee makes no small base dies. But will custom fit die if sized brass will not chamber.
I have used the 223 standard FL RCBS die for many years, no problems, in M16, Mini14, Ar180, T/C, M70, Savage Axis.
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