Headspace and OCD and the 280AI

Hello, so I am using the Hornady gauge tool. The base to the shoulder datum is 2.133 on most of the fired brass after resizing. Some are 2.134, 2.135, 2.136 and 2.137. Is that close enough or should work I towards getting them all exactly same? Factory Nosler unprimed is 2.130 and loaded precision hunter from hornady is 2.126.

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What I would do first is to find the correct size of the chamber, I would get the longest size of those fired brass ( not sized ) and chamber it to feel how the bolt will close, then try the next smallest fired brass (.001" size), see how it closes the bolt, then try the next smallest after that .( 002") if any. The size the bolt closes on with less resistance would be your chamber size and I would size them .001" - .002" smaller. It's what I normally do to find the best sizing length for my sized brass.

Since your brass are already sized, get the 2.137" sized brass in the chamber and close the bolt on it, does it feel tight? If it does, extract it, then try the 2.136", then the 2.135" and the 2.134" and see if any of those chambers without being too snug when closing the bolt. Maybe it seems maybe you are not bumping the shoulders back correctly.

You mentioned most of the fired brass is 2.133", I would adjust the full sizing die to bump shoulders back .002"

The measurement of the once fired cases is "usually" a good reference for where the shoulder should be on reloaded cases. I typically adjust my die so that the shoulder is about .001"- .002" shorter than this measurement.

Hope that helps.

I take 3 or 5 pieces of new virgin brass and fire it . then I neck size only , and fire it . then I neck size only , and fire it . I do this 2 or 3 or 4 times until I feel resistance when closing the bolt on neck sized brass . now I know the brass is fully expanded , for this chamber . I measure that brass off the shoulder with the tool , and it will all measure the same . then I set my die to bump the shoulder back .002" - .003" . I use the redding competition shellholder sets these give very consistent results . my fired brass length will be very consistent , and my resized brass length will be very consistent . when my resized brass length started to vary I would anneal my brass , now I anneal every time .


looking at your measurements , I think this must be once fired brass and it's not fully expanded . trying to set up on brass that is not fully expanded is not going to give the results you want . neck size and fire it again . if you don't have a neck size die , back off your full length die about 1/2-3/4 a turn . this should neck size without sizing the body .

It normally takes a few firings for brass to fully form / expand to a chamber; and jimbires's procedures are what I use for expensive brass, other than I haven't started annealing. Tackdriver284 is also correct, setting your FL die off of once fired brass is usually good enough and I do that for cheap brass and or gas guns to make sure everything runs smoothly.

To directly answer your question, there isn't anything wrong with having a few thousandths difference in shoulder position for bolt gun ammo. Usually factory ammo and virgin brass is undersized, so that it can function and form to any sized chamber and it usually shoots pretty well. I would be comfortable with your shoulders and I might consider marking the outliers (2.136 and 2.137 cases) to see when the shoulders stop moving on them, see if they cause any variations on targets / use them for fouling rounds.