Measuring Headspace for pre-fit shouldered barrel.

ajridgedell

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#1
I'm what you may call a hobby gunsmith. I chamber and thread my own barrels and occasionally for friends too. Normally I set my head space using the action. If I am going to make a "pre-fit" barrel without the action, what is the best way to measure from the shoulder to the back of the go guage? Obviously I will have the required dimensions of the action on hand. I have found using a depth mic placed on the back of the go guage and then coming down to the shoulder to be pretty inconsistent for me. I thought about making a tube that slides over the thread tenon and rests on the shoulder and comes out past the go gauge, so I can place my depth mic on the tube then measure down to the go guage. Interested to learn what works best for this measurement.
 

DAVETOOLEY

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#4
I made these for different lengths and diameter of tenons. It makes it very easy to measure to a few tenths. A depth mic and a separate stand alone collar will also work.
I used direct tenth reading thimbles but a $50 1 inch thimble off of EBay will work just as good.
 

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ajridgedell

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#5
I made these for different lengths and diameter of tenons. It makes it very easy to measure to a few tenths. A depth mic and a separate stand alone collar will also work.
I used direct tenth reading thimbles but a $50 1 inch thimble off of EBay will work just as good.
Wow thats pretty sweet!
 

Easy_E

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#7
Yeah pretty much, thanks! would it be better to go all the way to the shoulder? That way you measure from shoulder to case gauge and receiver face to bolt face?
I always figure the tenon length to head space measurement for my action so either measurement would work but the length has to be right on. I That ring would work better on Savage shanks I bet .
 

stangfish

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#8
It takes a different paradigm but if you measure case/gauge protrusion, breach face to shoulder length and thickness of lug and add to action face to bolt face it can be done with 2 tools at least it can be i my opinion.
1549927689100.png 1549927741400.png
 

ajridgedell

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#9
It takes a different paradigm but if you measure case/gauge protrusion, breach face to shoulder length and thickness of lug and add to action face to bolt face it can be done with 2 tools at least it can be i my opinion.
Thats what I have been doing, but when I place the depth mic on the back of the case guage and measure to the breach face I can easily get different results within a few thou if i place more or less pressure on one side of the mic as the go guage rocks back and forth in the chamber, even if i tape it up so its a snug fit. I made a collar to go over the thread tenon today that should work good. Thanks for the good ideas guys!
 

stangfish

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#10
Just an opinion but if your gauge is rocking enough to cause an appreciable amount of difference in your measurement you might consider checking the centerline of you tailstock with the centerline of your chuck. If you are doing it in a steadyrest then you need to sweep the rest in to be on axis with the tail stock.
 

DAVETOOLEY

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#11
Just an opinion but if your gauge is rocking enough to cause an appreciable amount of difference in your measurement you might consider checking the centerline of you tailstock with the centerline of your chuck. If you are doing it in a steadyrest then you need to sweep the rest in to be on axis with the tail stock.
It has nothing to do with alignment. Gages are under size. Enough to fit a chamber that has been cut with a roughing reamer. That's what I like about my method of measurement. The flat face of the thimble squares up the gage in the chamber. Using a collar with a depth mic does the same thing, just has more moving parts.
I will add that I like using my setup over a collar and depth mic because the face of the micrometer thimble is quite a bit larger than a depth mic. It should in theory result in more consistent measurements.
 

stangfish

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#12
Dave, There is no question your tools and setup is nice. Most hobby guys will not go to the trouble of purchasing the components to make that work....unless you are offering prints and sources.
 

DAVETOOLEY

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#13
Dave, There is no question your tools and setup is nice. Most hobby guys will not go to the trouble of purchasing the components to make that work....unless you are offering prints and sources.
I don't think cost is an issue. I just looked at EBay and a .0" -1.000" thimbles are available for under $40 shipped. A direct tenth reading thimble like I use for $59. That's just on the first page. For the hobbyist this a good project . It's not complicated enough that anyone can't draw it out in a few minutes and then go make it. I have a surface plate but it's easy to use a ground lathe bit to calibrate it.
 

ajridgedell

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#14
I don't think cost is an issue. I just looked at EBay and a .0" -1.000" thimbles are available for under $40 shipped. A direct tenth reading thimble like I use for $59. That's just on the first page. For the hobbyist this a good project . It's not complicated enough that anyone can't draw it out in a few minutes and then go make it. I have a surface plate but it's easy to use a ground lathe bit to calibrate it.
Can you add a link or what I should type in the search bar? I tried looking but I must not be using the correct wording in my search.