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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 8:00am
Originally posted by Frameman 1 Frameman 1 wrote:

That info illustrates that the 7.62 chamber is considerably longer than the .308.
I’m considering doing a chamber casting to help clarify the issue.

That should be an interesting exercise.
Look forward to seeing some conclusions.
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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 18 2020 at 8:12am
Originally posted by Frameman 1 Frameman 1 wrote:

I pulled the trigger for the Max 7.62 gauge. I’ll update when I have it.

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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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 8:17am
Originally posted by Frameman 1 Frameman 1 wrote:

That info illustrates that the 7.62 chamber is considerably longer than the .308.
I’m considering doing a chamber casting to help clarify the issue.
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote The Armourer Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 9:32am
Originally posted by Goosic Goosic wrote:

Originally posted by Frameman 1 Frameman 1 wrote:

That info illustrates that the 7.62 chamber is considerably longer than the .308.
I’m considering doing a chamber casting to help clarify the issue.
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.

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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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 10:21am
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 10:43am
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.
Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 11:01am
Sage advise...
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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 11:50am
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 12:49pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote The Armourer Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 12:53pm
Originally posted by Frameman 1 Frameman 1 wrote:

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?

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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Post Options Post Options   Thanks (0) Thanks(0)   Quote Frameman 1 Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 12:57pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote The Armourer Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 1:15pm
Originally posted by Frameman 1 Frameman 1 wrote:

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. .

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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Post Options Post Options   Thanks (0) Thanks(0)   Quote Frameman 1 Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 1:22pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 2:14pm
Originally posted by britrifles britrifles wrote:

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.  


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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Post Options Post Options   Thanks (0) Thanks(0)   Quote Frameman 1 Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 2:21pm
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote Frameman 1 Quote  Post ReplyReply Direct Link To This Post Posted: October 18 2020 at 2:28pm
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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