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Coin style head guage

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Honkytonk View Drop Down
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    Posted: January 09 2020 at 9:05am
My old friend the machinist (at work before I retired) called me for the specs of a coin style head guage. I had wanted him to make me a Foerster type, but he forgot about that (a little scatter-brained, but a great guy) and not wanting to look a gift horse in the mouth... By my measurements, the cartridge rim is .54" dia, (bolt face .57"). So I told him .54" dia x .074" thickness. He's going to take a .20" bite out of the .54" dia to clear the ejector. Sound about right?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: January 09 2020 at 9:08am
Oh ya. He's making it out of Peek material. It's a super tough "teflonish" stock used for bushings on rotating shafts.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Canuck Quote  Post ReplyReply Direct Link To This Post Posted: January 09 2020 at 10:07am
Sounds good to me. I would order a couple sets to have in my tool box. The fellow who used to make the older coin style gauges passed away I think a couple years ago. I managed to buy a set from him for the 303 and 7.62 x 54R.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: January 09 2020 at 10:34am
The guy who ran "Okie" is gone, but there is still one source:

Valmont firearms (UK)

Hi they are :

 

GO –0,064inch•NO GO –0,068inch• FIELD –0,074inch

 yeah we can post you a set be about £15 shipping £60 for the set

Lord Daniel Shallcross Valmont

Owner


www.valmontfirearms.net

www.valmontfirearms.com


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: January 09 2020 at 11:42am
This may be my inner "Bubba" coming out, but "Answer me this, Riddler!" I take a .303 British brass, full length size it, adhere the Peek (superteflon) disc I'm getting made as mentioned above, knowing that the adhesive (thinnest of epoxy, JB weld?) will add the tiniest amount of thickness to the now easier to install head space gauge? Thoughts?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote englishman_ca Quote  Post ReplyReply Direct Link To This Post Posted: January 09 2020 at 12:49pm
It would work but how solid would things be? 

The resistance to the closing bolt handle comes from the bolt trying to crush the gauge. Usually hardened steel is used, mainly for wear and for the repeatability of the gauging. Use it a thousand times and it does not crush or change dimensions.

I am not familier with the material of which you speak of by that name. Bushings and bearings are generally made from a material softer than the shaft they support. I can envisage some problems. But only one way to find out?....it's called prototyping!

Other methods? Measure a case rim and fit a feeler gauge in the gap at the rib and resistance shoulder on the bolt closed and pushed forward. Do some arithmetic to get head space. The head space clearance would be the thickness of feeler gauge..

I've seen one made from a hard washer done on a surface grinder. Almost the same as a coin gauge but no slot. And I once did see a regular hardware washer filed to size by hand. Well made and it measured up with calipers on .074 within +/- 1 thou.

There are tricks using feeler gauges cut up and stacked, glued, taped. Not a big fan.

But nothing is as reliable as a hard steel top hat type. No d**king around. Just pop it in like a cartridge, gently try to close the bolt. If it dont close, all good! Flip the rifle upside down, open the bolt, gauge falls into my hand.
Mine is made from hardened tool steel. It is harder than the extractor, so the extractor doesn't even leave a mark. I learnt the feel with the extractor pushing back. Finger tips on the knob, delicate touch required.

If you crank hard enough, just about any bolt will close on a field gauge.

Worth spending the money to get a good field gauge. Cry only once when you buy, it'll last you a life time.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: January 09 2020 at 2:50pm
Good points. Peek material is very tough. It takes a lot of hours (up to a year or three) to start it's wearing. On a properly aligned rotating shaft? I've seen bushings made of this stuff last 10 years. As mentioned, it's an experiment, and as far as I know, will be used on two rifles. JB Weld, in my experience, is not real forgiving, nor removable! I'll afix the Peek disc to a full length sized case, clamp, and then when adhered, buff the edges of the rim/coin. That brings me to another question. If a traditional Forster gauge doesn't have a slot cut out for the ejector, why would a coin style need it? Thanks all! I'll keep you posted!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: January 09 2020 at 3:29pm
I had this message sitting on my screen for a few hours, and before Englishman sent his reply.  Seems we are thinking the same thing. 
 
 
Hummm, PEEK (polyether ether ketone) has a very low modulus of elasticity compared to steel; not much higher than common plastics.  Not sure I would want to use this as a headspace gage.  You really want something fairly hard so you can "feel" when the bolt stops, you don't want that gage to compress at all.   
 
Not sure I follow the idea of bonding the disk to the case head? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: January 09 2020 at 3:46pm
I hear your concern on the material. My thought process to bond the coin to the cartridge was for ease of checking head space. Fiddling with s .070" coin trying to get it to stay in place on the bottom of a cartridge seems finicky. Hence, make it one piece.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: January 09 2020 at 3:57pm
HT, unless I'm missing something, you would have to cut/grind the full thickness of the rim off of a case if you wanted to add a .074 thick "washer" to make up a gage.  Or, do you mean measure the case rim thickness, then determine the thickness of PEEK "shim" to add up to the total 0.074 thickness of gage you want?  The epoxy will have some thickness, at least a few thousands. 
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zed Quote  Post ReplyReply Direct Link To This Post Posted: January 10 2020 at 1:09am
The Okie gauges are slightly magnetic; so stay on the bolt face. Very easy to use.
before I bought a set; I had rigged a temporary, single use head space gauge to check my rifles. Basically some industrial aluminium tape stuck onto the rear of an empty case. The tape can compress slightly when contact is made with the bolt head. Then measure the rim and tape thickness. It's a single use method.
I found that my rifle was close to the field limit, so invested in the Okie gauges. There is no real alternative to the proper tools. While my bodge head space gauge gave me a figure that was close; using the real gauges proved that it was not spot on! it was difficult to accurately measure the rim and tape accurately.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: January 10 2020 at 8:06am
The trick with coin gauges is to remove the magazine, place the rifle muzzle UP & insert the gauge from the bottom. After testing remove the same way.
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: January 10 2020 at 8:27am
Shamu. How does the cartridge stay in the chamber? I would have thought barrel down.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Honkytonk Quote  Post ReplyReply Direct Link To This Post Posted: January 10 2020 at 8:38am
Wow. I plead total ignorance! I've  useda full size Forster Gage before but... I just viewed a YouTube video on Okie gages on a Lee Enfield. It is just the coin, no cartridge. Man, do I feel stupid! The Okies must be the thickness of a rim plus .074" for the Field Gage. Is that correct?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Goosic Quote  Post ReplyReply Direct Link To This Post Posted: January 10 2020 at 9:34am
HT.  The Okey field coin gauge, like this one,is just .074" thickness, nothing else. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote britrifles Quote  Post ReplyReply Direct Link To This Post Posted: January 10 2020 at 10:37am
HT, the part you are missing is that headspace is defined as the distance between the bolt face (when locked and locking lugs of the bolt in contact with the receiver) and rear of the chamber for a rimmed cartridge.  For the LE, that maximum (field) is 0.074 inches.  The cartridge case rim takes up most of that space as it is intended to.  The minimum headspace must allow for the maximum rim thickness of a cartridge.  The maximum headspace relates to how much case web unsupported by the chamber is safe to fire.  
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