Documenting chamber measurements?

[Hannibal]

Most sammi drawing give the dia of the shoulder at the datum point a piece of steel with this sized hole drilled and bored square to parallel surfaces acts as a "Gage or new anvil for the mic giving a reading from the datum point to the case head. If made and set up with the headspace gauge to read 1.0000 over the headspace gauges marked size then a 1" bigger mic can be used for direct reading other wise a "constant" number is needed. This number is the difference between the gauges marked size and the mics actual reading. Like measuring a thread with thread wires the constant number bring thereading over the wires between the radiuos and vee to a actual measurement. If you have the thread and are making a new one then the comparative measurement from the existing thread to the one your cutting over the wires with out the constant number works. The above gage is a simple piece of steel 3/8" thick 1/2"-3/4" wide and 1" tall with the hole drilled in the center of the 3/8" thick area to a depth to clear shoulder and neck plus so free area but not thru ( have to have a solid area on top for mikes anvil to bear). Ideally start with 1"+ and work in with measurements over the headspace gage to where it reads the same +1" so a 1" bigger mic can be used and direst reading. This takes a little playing to get. Measure and mill surface with in .005+ and then grind or lap in to dead zero. If you decide to stamp the use on the side then do it before working in as stamping will stretch the metal and change size. Engraving is better for this. A piece of gage stock works well here and if desired can be hardened even.

Thank you. I appreciate the explanation.

[Hannibal]

If the ball matches the diameter of the datum line, its center will always be above the datum in an angled (conical) hole. The exact amount is depending on the angle - I'm afraid trigonometry must be applied here...

I had wondered about that, but couldn't decide if the conical hole would in fact hold the ball bearing above the datum. Thanks for the confirmation.

[Ballistics in Scotland]

I had wondered about that, but couldn't decide if the conical hole would in fact hold the ball bearing above the datum. Thanks for the confirmation.

There could scarcely be anything better for comparing chambers, including comparison with a test chamber known to be good, provided that the ball is of a size that rests on the true conical part of the shoulder rather than its front or rear edge. It could be a good method of arsenal quality control, possibly with a sort of long-snouted micrometer if it is for assembled rifles, measuring from either the rear face of the barrel or the locking lugs.

[nekshot]

just following this makes me wanna get a round bearing and do some measuring on these various 8 mm's during this hot humid weather. If nothing else I will look like a genius in a chamber depth debate until I open my mouth!