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The Armourer View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote The Armourer Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 2:49pm
Originally posted by Frameman 1 Frameman 1 wrote:

Using a fire formed 7.62 case essentially acts as a headspace gauge the protruding primer pushes the case against the chamber walls at the case shoulder. As the bolt is cammed forward into place the primer is forced further into the case.
The remaining primer protrusion is the head clearance gap.
This gap should be somewhat relevant.

Sorry, I just dont see it.

Yes your 'primer' is showing the head clearence, but, it is not showing headspace which is the measurement you are trying to take.
So your 'primer test' shows a a 0.005" head clearence - how do you translate that into a headspace reading  - where exactly do you measure from on the case taper back to the primer to get the headspace ?

I'm not sure how else to explain it but, the head space is the measurement taken at a specific diameter on the slope of the shoulder. Forcing a fired case into the chamber is showing (doing) nothing to actually identify :
a) The point where the measurement is taken
b) The dimension at that point

The case will be forced into the chamber by the camming action of the bolt, if it has expanded it will be forced into the chamber irrespective of where the shoulders were, or are, after firing.

On a Rimless round You can only measure headspace by using a headspace gauge.
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Frameman 1 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Frameman 1 Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 4:18pm
I wasn’t trying to find headspace by measuring the head clearance gap. I understand they are two different measurements. I was simply trying to find the clearance gap to see if the two measurements have any bearing on each other. I have the “coin” style headspace gauge for my Mosin Nagant rifles that measures from the breech face of the chamber to the bolt face. Which is a fixed point of the chamber. The distance between the shoulder datum to the bolt face is also a fixed point for rimless rounds. 
I am simply substituting the fire formed case with protruding primer to measure the same distance as an legit gauge. 
I realize this method isn’t as consistent or as repeatable as using a real gauge but might be an approximation that might be useful. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 6:24pm
All cartridge cases will lengthen upon firing unless the rifle chamber headspace and cartridge headspace is practically the same.  The brass cannot hold the pressure without restraint from the thick steel chamber.  The brass plastically deforms to fill the chamber upon firing.  When the chamber pressure drops, the case stresses will relax and the case will slightly retract based on the brass stress/strain relationship.
  
What you are measuring with the primer in a fired case is the amount the case relaxes after firing (plus the very small amount the bolt compresses under the thrust loads).  What you want to measure is “head clearance”, the distance between the bolt face and head of the case with the case fully forward in the chamber.  To so this, you must use a new unfired case.  I’d expect it will be close to .010 in your chamber.  

The Armourer is correct, that will not give you the actual headspace dimension in your rifles chamber, but will give you an idea how much the brass is straining under the first firing.  Excessive permanent strain is what causes case ruptures.  In a Long chamber, the damage is done on first firing, full length resizing cannot repair this damage. 





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Frameman 1 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Frameman 1 Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 6:33pm
I see what you gentlemen are saying. I will measure it with an unfired case.
Very interesting!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 19 2020 at 7:26pm
I highly recommend this Hornady case headspace gauge for those that reload. $42.00 here in the US available at most places that sell reloading supplies.  Calipers not included.

Comes with 5 bushings corresponding to the diameter of the datum reference on the case shoulder to measure case headspace (e.g. 0.400 inches for the .308/7.62 NATO cartridge).  For rim cartridges like the .303, it is very useful to set up your FL sizing die to minimize how much you set the shoulder back by first measuring a fired case, then adjust the die to shorten the case head to shoulder length by .002 to .004 inches.  A bit of trial and error when adjusting the die position in the press, but will significantly increase the life of the brass.  The chamber lengths on my No. 4 .303 rifles vary considerably, perhaps by as much a 0.05 inches, so I sort and resize brass for each rifle separately. 

I use this gauge to set the FL resizing dies on all my bolt action centerfire rifles.  Auto loading rifles should have dies set to fully FL size the case to standard cartridge dimensions to ensure reliable feeding and minimize chances of a slamfire or out of battery discharge.  For this, I use the simple cylindrical case length gauge from LE Wilson to set up the die.  





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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: October 20 2020 at 7:24am
I also have, use & recommend these.
They're especially good on rimless cases because the insert is sized to stop at the "datum point" on the case shoulder so you know the measurements are correct.
I would suggest using them with a digital caliper, not a dial though.
There is an adapter & a gauge to zero for its much easier with digital's push button zero.
I don't know about the Hornady version, I bought mine before they bought the makers out. Mine also came with another adapter & gauge set for bullet seating to ogive!
Very handy toy.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: October 20 2020 at 11:02am
How does it help to improve accuracy?
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britrifles View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 20 2020 at 11:32am
I don’t think these improve accuracy, they will make it easier to ensure you don’t excessively size the brass for the chamber of your rifle and thereby extend brass life.  For the .303, I believe that neck sizing as long as possible (until you feel resistance to locking the bolt) then minimal (partial) full length size just enough to push the shoulder back .002 to .004 inches will significantly extend the life of the brass.  With this approach, I’ve gotten about 50 reload cycles on my .303 brass (partial length resize about every 10 to 12 neck sizing cycles). 

The Wilson case gages are good to ensure reliable feeding in self loading rifles, I use them to check the first few cases coming out of the full length sizing dies.  Failure of the bolt to fully lock can ruin your day.  I like to be sure I don’t get a chambering problem during the rapid fire stages of the match.  

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: October 20 2020 at 12:29pm
Is it a tool that would benefit me?
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britrifles View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 20 2020 at 1:41pm
I think so Goosic.  I find it very useful.  And not expensive either.
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Goosic View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: October 20 2020 at 1:46pm
Natchez has one for $33.00.
I bought it. Expect me to ask you a bunch of questions now when I start to use it. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 20 2020 at 1:57pm
No problem Smile
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The Armourer View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote The Armourer Quote  Post ReplyReply Direct Link To This Post Posted: October 20 2020 at 3:50pm
Originally posted by <div><br></div><div>The Wilson case gages are good to ensure reliable feeding in self loading rifles,  </div><div><br></div>[/QUOTE

The Wilson case gages are good to ensure reliable feeding in self loading rifles,  

[/QUOTE wrote:



They are pretty good for 'batching' rounds with similar rim thickness  to give you consistent shooting.

They are pretty good for 'batching' rounds with similar rim thickness  to give you consistent shooting.

Also clearly show the difference in rim thickness between PPU and SAAMI cases. (PPU top)




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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: October 20 2020 at 4:14pm
My 308 brass is mainly Lake City, followed by Lapua, then Norma. 
I would like to start separating and using only the Lake City for my Remington, the Lapua for the fully dressed No4Mk1/2 and the Norma for everything else. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 20 2020 at 7:08pm
Originally posted by The Armourer The Armourer wrote:

Originally posted by <div><br></div><div>The Wilson case gages are good to ensure reliable feeding in self loading rifles,  </div><div><br></div></td></tr></table>
<div><br></div><div>They are pretty good for 'batching' rounds with similar rim thickness  to give you consistent shooting.</div><div><br></div><div>Also clearly show the difference in rim thickness between PPU and SAAMI cases. (PPU top)</div><div><br></div><div><img src=uploads/5736/Rim_Thickness_gauge.jpg height=614 width=355 border=0 /></div><div><br></div><div><br></div><div><br></div>[/QUOTE

The Wilson case gages are good to ensure reliable feeding in self loading rifles,  


They are pretty good for 'batching' rounds with similar rim thickness  to give you consistent shooting.

Also clearly show the difference in rim thickness between PPU and SAAMI cases. (PPU top)




[/QUOTE wrote:


The recess for the rim in the Wilson gage is much deeper than the rim thickness.  What you are seeing on the RP “SAMMI” case sitting below flush with the gage is not because of rim thickness, it is the case dimension from the head to the shoulder.  If you invert the case and insert it, you will see that the forward face of the rim sits well below the surface of the gage. 



The recess for the rim in the Wilson gage is much deeper than the rim thickness.  What you are seeing on the RP “SAMMI” case sitting below flush with the gage is not because of rim thickness, it is the case dimension from the head to the shoulder.  If you invert the case and insert it, you will see that the forward face of the rim sits well below the surface of the gage. 


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Frameman 1 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Frameman 1 Quote  Post ReplyReply Direct Link To This Post Posted: October 22 2020 at 3:48pm
Well today I received my 7.62 NATO Field headspace gauge and the Hornady case length insert (.400) 308 Caliber. 
I removed the firing pins and extractors from both my Ishapore rifles. Neither bolt would close with gentle pressure. They had about 3/16” to fully closed. I also used a once fired PPU 7.62x51 case and inserted it into the chamber of the rifle from which it was fired. The bolt closed with no resistance and when fully closed it had zero fore or aft movement. I’m happy with these results. Now I can start to build custom Ammo for each individual rifle. I will also be following a much more conservative powder charge formula.
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