View Full Version : Headspace questions
August 15, 2000, 06:56 PM
When a barrel has been set back and a new chamber reamed ideally are you trying to get the headspace set for minimum expansion of the cartridge? (if you are concerned with accuracy at all) How much expansion is acceptable? Does this expansion affect accuracy, or once the cases are fire formed does this in effect compensate for the extra space? My rifle is a M70 Win. and I have had an "accuracy job" done on it. Using the headspace insert on the Stoney point tool, I am getting .008 difference between a new Federal cartridge, and then the case fired in the chamber. What do you think? Thanks for your help....ol blue
August 15, 2000, 09:09 PM
If I understand the headspace deal correctly, the idea is to not have so big a chamber that the case can split open when it is fired, nor move forward enough that the primer can blow out. As long as you're in the "Go/NoGo" zone, all's well. (I guess it's obvious that if the chamber is too small, the cartridge won't go in far enough to allow closing of the bolt.)
Your best accuracy should be with cases fire-formed to fit your chamber. Once they are fire-formed, that's as close to perfect as you can get.
I suggest neck-resizing only when you reload. That doesn't disturb the fit. I set my dies to only resize about 3/4 of the case neck. My theory is that the least working of the brass means the least work-hardening or embrittlement. 3/4 is enough to hold the bullet in place in spite of recoil.
[This message has been edited by Art Eatman (edited August 15, 2000).]
August 16, 2000, 07:27 AM
Ol Blue, my first concern when chambering a rifle barrel is safety. The second is accuracy. I would expect a fired case to stretch about .008". I have some 6mm Rem cases here that I just fired day before yesterday in a Mauser that I rebarreled. The fired cases measure 2.242" and the SAAMI case length is 2.233" so it's a difference of .009". Unless the customer specifies absolute minimum headspace, I chamber all the rifles I build .001" longer or deeper than exact minimum to allow for differences in factory brass. One of these days I'm going to have to do some testing to determine if that .001" effects accuracy to any degree. It it does I haven't seen it. But, then I only test fire the rifles with factory ammo. George
August 17, 2000, 02:47 PM
Thanks guys, You have helped to set my mind at ease a little bit. Always something to worry about!...ol blue
August 19, 2000, 02:06 PM
By the way George, is there somewhere on the net to look up SAAMI specs? I would be interested in what the SAMMI case length and max headspace measurement is for the .308 Win. Thanks...ol blue
August 19, 2000, 06:15 PM
[This message has been edited by sensop (edited August 19, 2000).]
August 20, 2000, 07:31 AM
Ol Blue, I think the info might be on Sierra's website at http://www.sierrabullets.com/ but for the .308 Win OAL = 2.015"; go gage length is 1.630". The headspace is measured from a "datum line" midway between the shoulder (1.560")and the neck (1.710") to the face of the bolt. George
August 20, 2000, 04:26 PM
Thanks George!....ol blue
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