I assume that most folks who are using brass fired once or more in their chambers without resizing are looking for maximum precision, possibly to run closer to the lands than I am intending to do here?
Anal- retentive level - get Unknown Munitions to make one from your own fireformed brass.
A modified case made from any brass we have here in the shop. Each modified case purchase will come with your choice of in stock bullet. If your cartridge has a standard bolt face (+/- .470), it is Standard fee. If your cartridge has a magnum bolt face (+/- .540), it is a Magnum fee.…
www.unknownmunitions.com
Hard to find stuff/ New chamber/ Something I don't have brass for - buy a COAL case from Unknown Munitions, even though it's not formed
Easy to find stuff - Get a Hornady Case
DIY - Drill out a case that you have
Also DIY - Cut a slit in the case neck
Using the tool:
Maximum attention to detail - run a headspace comparator on the COAL case and a fully formed case. Account for that difference in BTO. COAL Case - BTO 2.940, Shoulder 1.750. Resized, Shoulder 1.755. Add 0.005" to the BTO, use 2.945" to account for the gap between the case head and bolt face that fully formed brass won't have, which comes from shoving the undersized COAL case forward into the shoulders of the chamber.
Functional method - Call the headspace difference in formed and unformed shoulders NBD, move on with life because the difference in being 0.005" and 0.010" off the lands doesn't matter a hoot, start back at 0.020" off so you don't stick a bullet in the bore and miss a shot. Hunting gun, bench gun, comp gun, doesn't matter what kind of gun, IMO if you have to be within the first hundredth off the lands I don't want to shoot it and I'll go looking for a deeper node.
Here's the real kicker - it doesn't matter at all. As long as you work up your powder charge and as long as the bolt closes, does seating depth as a measurement matter? Not for anything other than repeatability. The only point of "finding the lands" is to find the longest you'd load to. The "distance to lands" measurement ceases to have any relevance once you pick your starting point. So don't get hung up on wanting to be a certain distance off, work on being where the thing shoots good. The measurements help quantify testing and structure the process so you don't waste components finding a good depth, the 0.020" off rubric is a common starting point, but there's nothing about any measurement that makes it better or worse than another.
As long as you don't accidentally jam a bullet by not paying attention, other methods that work just as good for a starting point: use book COL from the bullet manufacturer, use the BTO of a factory loaded round, or use where the base of the bullet seats at the shoulder, then you work longer.