Headspace question

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Ranman

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I just bought an RCBS precision mic guage for a 30-06 and measured some fire formed brass. I found the brass about .002 shorter than the Zero minimum. Unfired brass that I bought was about .003 shorter. Assuming that the guage is accurate, it would seem that my Tikka T3 would have a tight chamber yet I've not had problems chambering ammo. Is this typical, and is it something that I should be concerned about for safety???
Thanks
Randy
 
Measure your once fired brass after you resize it. A growth of .001 in length for a first firing would not be unusual or tell you much related to safety. You regulate the length of the brass by trimming, usually to about .010 less than maximum case length established by manufacturing specs. The length of the fired case may have no relationship at all to your chamber as it should not reach the limits of your chamber throat before or after firing. Consequently I have no idea how you conclude your rifle may have a tight chamber from that single measurement.
 
I'm talking about headspace measurement....length from head to datum line on shoulder, not the overall case length.
Randy
 
Ranman said:
I just bought an RCBS precision mic guage for a 30-06 and measured some fire formed brass. I found the brass about .002 shorter than the Zero minimum. Unfired brass that I bought was about .003 shorter. Assuming that the guage is accurate, it would seem that my Tikka T3 would have a tight chamber yet I've not had problems chambering ammo. Is this typical, and is it something that I should be concerned about for safety???
Thanks
Randy
Click to expand...

Old mate, are you taking the zero minimum from the RCBS mic or are you taking it from a head-space guage, as in are you working solely from the RCBS mic measurements ?
As an aside, your fired cases are .001" longer than unfired cases, which is terrific......more importantly what size are the cases AFTER you have full length sized them, I ask this because the sole use that I can see for the RCBS mic(with-out a head-space guage), is in the setting up of dies.
If the measurement is .002" or smaller, hit your knee's, thank God, then go shooting !
 
Thanks for the reply. I was talking about the measurement taken from the RCBS mic guage. After full length resizing the brass the head to shoulder length actually increases by .003-005. Thats with the die all the way down to the shellplate. I thought that should shorten it, so I'm still a bit confused as to how I should adjust the die. Thanks for the input
Randy
 
Ranman,
After you full length resize your brass try them in your rifle and see if they chamber properly.
It goes without saying that you have not yet primed or loaded any cases when you try them in your chamber.
257 Roberts
 
257Roberts is right, you shall have to try the sized cases in the firearm before you can go any further.
Just a point though, the chamber in your die, firearm and mic are all different, you have to strike a happy medium.
Also, when you try the empty, sized cases in your firearm you may want to remove the firing pin assembly from the bolt so that you can feel any pressure exerted on the bolt-head from the case.

And pray that you do not have a long die, not a problem though as it can be machined if absolutely necessary.
 
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How much resistance did you feel when you withdrew the neck sizer button back through the case? If a lot you can stretch a case. If this is happening you should be lubing the inside of the case neck, assuming you haven't been. Either case lube lightly applied or Motor mica which is dry. As stated though, check an unprimed case for fit in the rifle.
 
The brass does fit into the chamber with no problems (before and after resizing). I emailed RCBS for some advice and they replied that the brass has to be fired a couple of times before it will be expand to completely fill the chamber. I suspect that this must be the case and that the fire formed brass is not yet a true representation of the chamber. That brass had been fired twice before, once was a factory load and the second was a load I'm working up that is about 10% less than max. Maybe the charge wasn't great enough to fully expand the case to chamber dimensions.
Thanks again for the thoughts guys
Randy
 
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