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Head space gauge

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Macd View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Macd Quote  Post ReplyReply Direct Link To This Post Posted: January 27 2018 at 4:58pm
I trust no one will take offense to me adding a few words that will be old news to the experienced members.   Many times new shooters read these forums and this is for their benefit.

Headspace is often a misunderstood concept. Brownells has a really good technical article on the subject (Google it) and the proper use of headspace gauges just as Shamu has explained above.  Passing a field gauge is fine for most unfired brass but you increase your chance of case separation with even the second firing as the brass has likely been subject to excessive stretch on the first firing.  The LE is already reputed to be hard on brass.  Military chambers were designed to accept cartridges with generous manufacturing tolerances and in varying conditions of cleanliness.  As long as the round fired and the empty case extracted the resultant condition of the fired case was unimportant.  Neck sizing, annealing necks and avoiding high pressure loads can help prevent premature case failure.  You can also measure rim thickness of cases and choose only those with the thickest rims.  The minimum rebate in the chamber for the rim is .064" but you will find brass with rims that are well under this thickness.  Fortunately correcting a headspace issue may be quite simple in the LE just by swapping out to a longer bolthead.    If you are at the longest bolthead already then a barrel setback and re-chambering is needed.   You will read about "home remedies" like putting an o-ring or other spacer ahead of the rim to effectively increase rim thickness or soldering a thin washer onto the bolt head.  I have no experience with these "fixes" but it sounds like using pantyhose to replace a fan belt.  It may work but I would avoid unconventional solutions.

Will excessive headspace lead to a kaboom or other catastrophic failure?  Not in my experience.  It will lead to case separation, venting of gases and require removing the remaining part of the case from the chamber.  It is also hard on the bolt and locking lugs/receiver channels.   A prudent rifleman will remove the bolt and inspect the barrel to confirm it is clear.

Safe shooting.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: January 28 2018 at 3:08pm
Macd makes some good points, but even more is relevant.
Rimless cases headspace totally differently from rimmed ones & it causes some confusion when the two are intermingled.
Generous chambers can happen even with tight headspace & vice-versa so its important to understand how they both inter-relate.
There's a .PDF I posted years back on headspacing for reloaders & the early part is pretty helpful on them, even if you don't reload.
Let me see if I can find it. There were 2 versions a pre-photobucket crash (with all the images lost) & a post disaster one with them.

I think (hope) this is correct version.

uploads/3/smoking_cases.pdf
Yup, this is it.
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 Macd Quote  Post ReplyReply Direct Link To This Post Posted: January 28 2018 at 3:52pm
Excellent paper Shamu.  Since this is a LE rifle forum we won't get into handgun cases unless someone really wants to Tongue.  Weatherby and other belted cases are another story too.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Link Quote  Post ReplyReply Direct Link To This Post Posted: January 29 2018 at 3:31am
Very good!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: February 05 2018 at 6:03am
I have a friend that is an awesome machinist. He is set to retire soon so I'd like to abuse him. I know a bit about headspace measurements. But do not have gauges as a gun store in town has some. If I brought my machinist friend an empty fresh resized 303 brass, could he duplicate that with a solid aluminum (he had access to slot of different materials) dummy and add .074 or Field measurement on to the rim? It sounds simple (for him) I must be missing something. I wouldn't think the ejector would be an issue, but again, looking for some sage advice. Thanks.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Link Quote  Post ReplyReply Direct Link To This Post Posted: February 05 2018 at 7:17am
Try looking at Okie's headspace gauges.  Since the .303 Brit is a rimmed cartridge they made the "coin" type gauge.  Look at these:  http://www.okiegauges.com/sales.html You'll see they have a cutout for the ejector.  Here's the info Shamu provided back on page 1.

The OD measures:
0.53515" for the 1-dot GO = 0.064"
0.5350" for the 2-dot NO-GO = 0.067" 
0.5350" for the 23-dot FIELD = 0.074"
Measured across the sides so the cut for the extractor doesn't factor in.

Put your friend to work.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: February 05 2018 at 7:32am
Will do! Thanks!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Macd Quote  Post ReplyReply Direct Link To This Post Posted: February 05 2018 at 7:34am
Originally posted by Honkytonk Honkytonk wrote:

I have a friend that is an awesome machinist. He is set to retire soon so I'd like to abuse him. I know a bit about headspace measurements. But do not have gauges as a gun store in town has some. If I brought my machinist friend an empty fresh resized 303 brass, could he duplicate that with a solid aluminum (he had access to slot of different materials) dummy and add .074 or Field measurement on to the rim? It sounds simple (for him) I must be missing something. I wouldn't think the ejector would be an issue, but again, looking for some sage advice. Thanks.


Would look like this Forster gauge.  Read use here.

https://www.forsterproducts.com/pdf/instructions/Headspace_Gage_Instructions.pdf


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: February 05 2018 at 8:33am
Yes! That's what I had in mind! Any opinions as to it or the discs work better? The same? Thanks!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: February 05 2018 at 9:02am
I prefer the discs. Frankliy the problems of twisting sliding & so on a plug type gauge is something I prefer to avoid.
Lets face it with a rimmed case all you need is the rim, nothing else counts.
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: February 05 2018 at 10:00am
I believe I will go with the discs. Thanks!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Link Quote  Post ReplyReply Direct Link To This Post Posted: February 05 2018 at 11:01am
Seems like the disc would also be easier.  I look forward to seeing what he can do.  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: February 05 2018 at 1:36pm
Basically yes. Get a rod of the diameter needed, run a key-way down one side, drill a center-bored hole & part off to length.
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 Link Quote  Post ReplyReply Direct Link To This Post Posted: March 19 2018 at 2:01am
Good mornin',
Just wondering if Honkytonk's machinist friend has considered this endeavor?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ranch Dog Quote  Post ReplyReply Direct Link To This Post Posted: March 19 2018 at 4:14am
I would be interested in purchasing a set of "Okie" style discs as well. I wish I would have bought a set. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: March 19 2018 at 4:42am
Its a shame but Okie was a one man band & he's passed on now.
There's a definite niche market for these now so its time for HONKYTONK's buddy to jump in with a precise quality product.
Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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