Measuring headspace/bullet seating with Hornady tool

Discussion in 'Reloading Forum (All Calibers)' started by mousegunner, May 15, 2019.

  1. mousegunner

    mousegunner

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    Once you install the body on your calipers and install the headspace/bullet comparator you close and zero the calipers correct?

    Is the edge that touches the datum on the shoulder flush with the face of the insert? Or is it recessed into the insert. Same with bullet comparator.

    I'm just curious if once you zero the calipers it's a true zero to where the case or bullet is touching and measured.

    Do the Sinclair inserts give a better feel than the aluminum Hornady inserts?

    I'm using a RCBS case mic but wanting something I don't have to screw/unscrew. Thanks for looking.
     
  2. Ned Ludd

    Ned Ludd Silver $$ Contributor

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    The comparator insert for the bullet will seat somewhere on the bullet ogive close to the point that will first contact the rifling. Exactly where the bullet comparator insert seats depends on the actual diameter of the hole, which can vary. The headspace comparator should index on the middle of the shoulder.

    Whether you're getting a "true" zero with any comparator tool is questionable. However, it doesn't matter because some of the measurements we use are relative at best, not direct. For example, we're not directly measuring the distance from the bolt face to the bullet contact point in the chamber throat. However, we can use our comparator tools to get a reasonable reference measurement. Whether that reference measurement is accurate to +/- 0.0005" or +/- 0.005", it is treated as though it is infinitely accurate. Once you start directly measuring the dimensions of loaded rounds and shooting them at targets to determine which dimensions provide the best accuracy/precision, it no longer matters much whether the reference point measurement was spot on, or a few thousandths off. Frankly, you could even use the caliper inserts without actually zeroing the caliper, as long as you did it that way every time, and it wouldn't change anything.
     
  3. McGraw

    McGraw Silver $$ Contributor

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    I have one Sinclair 6.5 insert and the rest are the Hornady kit. The Sinclair is stainless steel, I think. It’s not chamfered like the Hornady ones and truthfully gives me fits because it’s tight and grabby, although it could be more precise. That’s just my experience.
     
  4. Texas10

    Texas10 Gold $$ Contributor

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    Since there are no standards guiding the manufacture of hand loading gages like the ones you describe, any measurement you get is useful to you and only you, and is not an absolute dimension. You can pick out three different headspace gages and you'll get three different measurements on the same piece of brass.

    As to your question about zeroing out the caliber, yes, zero it out when fully closed and the dimension you get will be easily repeatable, as long as you use that particular gage set. Some gages are bored at an angle to match the shoulder angle, but if it doesn't match it exactly there is potential for error. The chances that the chamber, sizing die (not counting spring back) and gage will all have the exact same angle is about a million to one, IMOP.
     
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  5. jpx2rk

    jpx2rk

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    I ended up purchasing a set of calipers for each tool (headspace and bullet comparators) so I wouldn't have to bother with swapping them out. I do zero the calipers with the tools/caliper jaws closed. My Hornady headspace comparator is slightly radiused ,while the bullet version is not.
     
  6. bsekf

    bsekf

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    The Hornady tool shoud have instructions telling you which insert to use. The measurement will be relative. The same as when using the tool to measure CBTO.
     
  7. jepp2

    jepp2 Gold $$ Contributor

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    As mentioned by Ned, I don't bother with zeroing my calipers. But I have written down what each should measure on my caliper. So I'm off by ~2.003" on all my measurements, but it is just a relative measure, so it isn't important.

    I personally like the bump gages by Whidden the best. They have a chamfer on the inside edge of the gage, and I believe it will remain consistent over the life of the gage. The Hornady gages have a fairly sharp edge, and as I rotate cases, it is taking the sharp edge off. But in using them for about 10 years, it hasn't changed yet.

    Here is the link and a picture of the Whidden gage.
    https://www.whiddengunworks.com/product/shoulder-bump-gauge/

    Whidden Gage.jpg
     

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