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The Armourer
Senior Member Joined: June 23 2019 Location: Y Felinhelli Status: Offline Points: 1246 |
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That should be an interesting exercise. Look forward to seeing some conclusions.
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Goosic
Senior Member Joined: September 12 2017 Location: Phoenix Arizona Status: Offline Points: 8792 |
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MIXING AND MATCHING BRANDS OF HEADSPACE GAUGES - Don't do it!! That's the short answer, here's why. It boils down to tolerance stacking. Each Headspace Gauge manufacturer works within a range specified by SAAMI. Manufacturer "A" may work at the high end of the range while Manufacturer "B's" gauges are in the middle of the tolerance range. Mixing the two could give an inaccurate reading. By sticking with one brand within a particular caliber, you will eliminate a variable. If you have a Forster, .308 GO gauge, get a Forster, .308 NO GO. Use Clymer with Clymer and Manson Precision with Manson Precision, etc. You can use any brand of headspace gauge with any other brand of chambering reamer. e.g. Forster Headspace Gauges with Clymer Reamers, Manson Precision Gauges with JGS Reamers, etc.
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Goosic
Senior Member Joined: September 12 2017 Location: Phoenix Arizona Status: Offline Points: 8792 |
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DiamondKBrass.com sells certified once fired 7.62x51mm NATO brass and brand new and primed Lake City 7.62x51mm NATO brass. The prices are amazing for the once fired stuff.
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The Armourer
Senior Member Joined: June 23 2019 Location: Y Felinhelli Status: Offline Points: 1246 |
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Good advice. As shown by manufacturers making 'brass' to SAAMI specifications - most of them work to the 'bottom half' of the tolerance limits. Rim thickness on 303 is specified as 0.064" + zero, - 10 thou (0.064 max and 0.054 min) The majority of Win, Rem etc is below 0.058 (but batches vary) whilst the likes of PPU are up around 0.060" - o.o62" Comparison of unfired Win 303 and a PPU 303 - case wall thickness and secondly same manufacturers rim thickness |
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Honkytonk
Senior Member Joined: December 30 2017 Location: Brandon Mb Status: Offline Points: 4770 |
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I am sold on PPU brass for my .303's. I've reloaded each of the first 100 I bought at least four times and they still look great. Got a brand new bag of 100 I haven't even touched yet. Never had that kind of longevity from Winchester or Remington.
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Shamu
Admin Group Logo Designer / Donating Member Joined: April 25 2007 Location: MD, USA. Status: Offline Points: 17603 |
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Respectfully to all involved. You can not compare rimmed to rimless brass. The working of the brass during firing is so different such comparisons are misleading at best. Compare apples to apples & oranges to oranges for more meaningful results is my suggestion.
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Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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Honkytonk
Senior Member Joined: December 30 2017 Location: Brandon Mb Status: Offline Points: 4770 |
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Sage advise...
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Frameman 1
Senior Member Joined: July 30 2019 Location: SW Ohio Status: Offline Points: 382 |
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I’ll risk a bit of flaming with this measurement. Since I don’t yet have a headspace gauge I decided to check the head clearance. I used a 7.62 NATO once fired casing and removed the primer without resizing of any kind. I took a case length measurement then partially reinserted the primer , closed the bolt on this case and removed and measured again for length. I came up with 0.005” difference.
This sounds to be a pretty small clearance gap. Anyone have any thoughts on this?
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There are no Americans in Baghdad!!
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britrifles
Senior Member Joined: February 03 2018 Location: Atlanta, GA Status: Offline Points: 6539 |
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You should use a new 7.62 case. The fired case has already been elongated to fit the chamber, minus the brass relaxation after firing.
I’m not a fan of buying once fired 7.62 cases, they may have been fired in long 7.62 NATO chambers and already have thinned case walls from stretching. Midway has a very good deal in new NAMMO 7.62x51 cases, $30 for 100 cases. I don’t think you will get an accurate headspace measurement from a chamber cast. |
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The Armourer
Senior Member Joined: June 23 2019 Location: Y Felinhelli Status: Offline Points: 1246 |
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I could be misunderstanding, but what you look to have done is 'replicated' measuring the rimmed case headspace. What you have done is measure the gap between the rim and the front of the bolt head by measuring the distence the primer is NOT pushed in. On a non-rimmed case the headspace is part way down the neck of the chamber (somewhere between the 2 shoulders) I don't think you can measure that using a primer - you need to measure the diameter of the chamber where an unfired case (not stretched) touches the circumference of the neck at the correct point,
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Frameman 1
Senior Member Joined: July 30 2019 Location: SW Ohio Status: Offline Points: 382 |
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no not exactly.
What I am measuring is the gap behind the she!! case a the bolt face. I believe this is referred to as bolt head clearance. .
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There are no Americans in Baghdad!!
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The Armourer
Senior Member Joined: June 23 2019 Location: Y Felinhelli Status: Offline Points: 1246 |
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Correct, which is part of the function of headspace on a rimmed cartridge, but is meaningless for a non-rimmed cartridge.
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Frameman 1
Senior Member Joined: July 30 2019 Location: SW Ohio Status: Offline Points: 382 |
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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.
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There are no Americans in Baghdad!!
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Goosic
Senior Member Joined: September 12 2017 Location: Phoenix Arizona Status: Offline Points: 8792 |
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I do not see an immediate issue if the certified once fired 7.62x51mm NATO brass is full length resized, prepped accordingly, and then neck sized after firing for that particular rifle.
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Frameman 1
Senior Member Joined: July 30 2019 Location: SW Ohio Status: Offline Points: 382 |
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I agree with britrifles that a chamber cast would be very difficult to determine headspace but would serve to expose throat erosion, and bullet jump.Besides I’m bored and want to try something new to me😎
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There are no Americans in Baghdad!!
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Frameman 1
Senior Member Joined: July 30 2019 Location: SW Ohio Status: Offline Points: 382 |
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Using a new case as opposed to a fire formed case to check head gap clearance would be an interesting comparison.
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There are no Americans in Baghdad!!
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