Fire-forming .223 -- Necesary for accuracy?

Lilswede1 · December 13, 2008, 09:38 AM

If once-fired-cases headspace is too long and is then re-sized to fit a specific rifle (.223 CZ 527 bolt) allowing .002" headspace would this be the same as fire-forming the case?
Also, if the headspace of a case is short by .004 - .006" how much will this affect the accuracy of that round if the OAL of the bullet is coorect for that rifle.
Yes, I could and will find this out for myself at the range but some of you may be able to save me a lot of time and shooting.

Alleykat · December 13, 2008, 09:41 AM

The case's being "too long" has nothing to do with headspace...kind of lost interest after that first sentence.

Lilswede1 · December 13, 2008, 06:55 PM

Hope i was am make my question a little more understandable.

rn22723 · December 13, 2008, 08:48 PM

You are over thinking too many things. Just FL size the brass if this the once fired brass you have been talking of. Then once you fire that lot of brass in the CZ it is Fire Formed and if you take care and neck size that lot of brass you should have decent accuracy potential. You are really over thinking some of this, and your using the term head space is not making thinks very clear for most readers.

jhansman · December 13, 2008, 09:49 PM

I would only add that when you necksize, be sure you get decent tension on the bullet. If you can push the bullet into the case with your thumb after seating, you need more tension on your neck sizing die. Until I figured this out, I was getting incomplete powder ignition, crazy flyers, and damn ugly brass.

**Unclenick** · December 13, 2008, 09:49 PM

A fired case has expanded to fill the chamber it was fired in. That is fireforming of the case. At normal chamber pressures, a cartridge which starts out smaller than the chamber will spring back slightly from full chamber size after firing, but is very close to mirroring the headspace of the chamber.

If you measure a once-fired case from its casehead to the headspace intercept on the case (close to or at mid-shoulder for rimless bottleneck cases), that will be very close to your chamber's headspace measurement. Make this same measurement for both a once-fired case from another gun and a once-fired case from your gun. It will show whether the first case was fired in a chamber with longer or shorter headspace than your own gun has. If the fired case from the other gun is longer than a fired case from your gun, it will have to be full-length resized before firing in your gun or it won't fit. If it was fired in a gun with shorter headspace than yours has, it may fit your gun without full-length resizing if that other gun's chamber also was not wider than your own. In this case you can neck size the case and fire it to fireform it to your own gun's chamber.

As to accuracy, shooting a case fireformed in your gun will force better alignment of the bullet with your bore axis than a full-length resized case can offer. That will be most apparent at longer ranges, but can be seen at 100 yards in an accurate rifle.

December 13, 2008, 09:38 AM	#1
Lilswede1 Senior Member Join Date: September 8, 2008 Location: NW Wash State Posts: 216	Fire-forming .223 -- Necesary for accuracy? If once-fired-cases headspace is too long and is then re-sized to fit a specific rifle (.223 CZ 527 bolt) allowing .002" headspace would this be the same as fire-forming the case? Also, if the headspace of a case is short by .004 - .006" how much will this affect the accuracy of that round if the OAL of the bullet is coorect for that rifle. Yes, I could and will find this out for myself at the range but some of you may be able to save me a lot of time and shooting. Last edited by Lilswede1; December 13, 2008 at 06:53 PM.

December 13, 2008, 06:55 PM	#3
Lilswede1 Senior Member Join Date: September 8, 2008 Location: NW Wash State Posts: 216	definition of terms Hope i was am make my question a little more understandable.

December 13, 2008, 09:49 PM	#5
jhansman Senior Member Join Date: June 17, 2007 Posts: 680	I would only add that when you necksize, be sure you get decent tension on the bullet. If you can push the bullet into the case with your thumb after seating, you need more tension on your neck sizing die. Until I figured this out, I was getting incomplete powder ignition, crazy flyers, and damn ugly brass. __________________ Blessed is the man who has nothing to say, and cannot be compelled to say it.

December 13, 2008, 09:49 PM	#6
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	A fired case has expanded to fill the chamber it was fired in. That is fireforming of the case. At normal chamber pressures, a cartridge which starts out smaller than the chamber will spring back slightly from full chamber size after firing, but is very close to mirroring the headspace of the chamber. If you measure a once-fired case from its casehead to the headspace intercept on the case (close to or at mid-shoulder for rimless bottleneck cases), that will be very close to your chamber's headspace measurement. Make this same measurement for both a once-fired case from another gun and a once-fired case from your gun. It will show whether the first case was fired in a chamber with longer or shorter headspace than your own gun has. If the fired case from the other gun is longer than a fired case from your gun, it will have to be full-length resized before firing in your gun or it won't fit. If it was fired in a gun with shorter headspace than yours has, it may fit your gun without full-length resizing if that other gun's chamber also was not wider than your own. In this case you can neck size the case and fire it to fireform it to your own gun's chamber. As to accuracy, shooting a case fireformed in your gun will force better alignment of the bullet with your bore axis than a full-length resized case can offer. That will be most apparent at longer ranges, but can be seen at 100 yards in an accurate rifle. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

December 13, 2008, 09:41 AM	#2
Alleykat Junior member Join Date: July 26, 2007 Posts: 3,668	The case's being "too long" has nothing to do with headspace...kind of lost interest after that first sentence.

December 13, 2008, 08:48 PM	#4
rn22723 Junior member Join Date: December 10, 2001 Location: Burbs of Minneapolis Posts: 676	You are over thinking too many things. Just FL size the brass if this the once fired brass you have been talking of. Then once you fire that lot of brass in the CZ it is Fire Formed and if you take care and neck size that lot of brass you should have decent accuracy potential. You are really over thinking some of this, and your using the term head space is not making thinks very clear for most readers.