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Cas City Forum Hall & CAS-L  |  CAS TOPICS  |  Gunsmithing  |  Topic: Measuring 1873 rifle headspace 0 Members and 1 Guest are viewing this topic. « previous next »
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Abilene
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« on: July 13, 2017, 04:20:13 pm »


Question for some of you gunsmithies.  How does one measure the headspace on a '73 rifle?  I have heard before of using feeler gauges, maybe even heard of someone saying automotive feeler gauges would work.  I have a set of those, but how do you get the gauge into the space between the bolt face and the cartridge?  Do you cut a thin strip off the gauge and/or bend it?  Removing the extractor would make it easy to insert the gauge from the top but I'd rather not do that.

I've used the "poor man's" method of putting a piece of brass into the chamber that has a used primer sticking out the bottom, barely inserted into the primer pocket, then closing the bolt on the brass and letting it seat the primer.  The amount the primer still protrudes from the base is the headspace.  This is easy and gives some info, but is difficult to get an accurate measurement.
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Coffinmaker
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« Reply #1 on: July 13, 2017, 06:23:06 pm »

I know!!  I know!!  I Know!!! Call me!! Call Me!! Call me!!  OK ... I ... got it.

Two best ways.  First the Bestest Easiest Way.  Shop around for some good "TAPERED" feeler Gages.  Of course, the tapered gage MUST fit between the extractor and mortice side wall.  Insert the blade with the action slightly open, then close the action, trapping the gage between the bolt face and the cartridge base.  I suggest you also use a de-primed case.  If your chosen blade will not allow the action to close ..................

Second best way.  With a standard constant width Feeler gage set, clamp the blades tightly closed.  With your terrible and dangerous Dremel Tool, grind away one side until you have a reduced with blade that will slide past the extractor.  You may have to lightly dress the side you have ground.

Optimum Head Space is .004 at +/- .001  Some rifles will still function say out to some really ridiculous head space however I recommend it be corrected.  In most instances, you will find too much head space in large bore rifles and too tight in small bore guns.  Fixing the head space is the really fun part.

Coffinmaker
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Abilene
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« Reply #2 on: July 13, 2017, 06:59:18 pm »

Thanks for the info.  About how narrow does the gauge need to be? 

Trying to measure my 32-20.  I think it is on the high side, which was verified by Ryan, a gunsmith for Cimarron, when he adjusted the extractor on the then-new rifle which was having trouble extracting since Uberti doesn't adjust the .357 bolts and extractors for the smaller rim.  But he didn't give me a measurement.  It has been functioning fine, but I'm thinking this is a good excuse to get my 1st short stroke kit, which would be a C&I 3rd gen. made to tighten the headspace.
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August
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« Reply #3 on: July 13, 2017, 07:56:03 pm »

measure with pieces of paper, stacked to the necessary thickness.  Then, measure the paper with a caliper.
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Pettifogger
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« Reply #4 on: July 13, 2017, 08:36:47 pm »

Go here and scroll down to page 112.  Headspace on . 32-20 is .065 miniumum and .072 msximum.  Measure the thickness of the rim of the shell you are using and then go from there with your shims.  So, if your rim is .060 thick you should be able to insert a .005 shim.  You should not be able to insert a .013 shim.


http://saami.org/specifications_and_information/publications/download/Z299-4_ANSI-SAAMI_CFR.pdf#page=13



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Coffinmaker
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« Reply #5 on: July 13, 2017, 08:58:33 pm »

Gotta Dial Caliper??  Measure between the extractor and the mortice wall.  Almost forgot.  Measure the head space of BOTH sides of the Breach Block.  The face of the breach block is often NOT machined square.

Coffinmaker
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Abilene
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« Reply #6 on: July 14, 2017, 02:56:49 pm »

Thanks for all the tips!
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Malamute
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« Reply #7 on: August 15, 2017, 11:13:45 pm »

Go here and scroll down to page 112.  Headspace on . 32-20 is .065 miniumum and .072 msximum.  Measure the thickness of the rim of the shell you are using and then go from there with your shims.  So, if your rim is .060 thick you should be able to insert a .005 shim.  You should not be able to insert a .013 shim.

http://saami.org/specifications_and_information/publications/download/Z299-4_ANSI-SAAMI_CFR.pdf#page=13


 ^^^ This. The part about measuring the rim of the shell you are using is nearly always left out of descriptions of this. That would assume the rim of every shell is perfect, which they will not be, nor will they all be exactly the same. Ammo is often made towards the  minimum end of specs for headpsace so it works in all guns. Also keep in mind, headspace isnt an exact number, its an acceptable range of size in both ammo and gun. A gun at the higher end and ammo at the lower end of spec, and measuring the difference, isnt really telling you much unless checking the rim and taking that into account.

 Many also get upset when they see primers backing out, when the gun may be in spec, just not enough pressure to push the primer back into the case as happens with higher pressure loads.
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