I was debugging some primer seating issues related to my seating depths and headspacing on my reloads. Thought I was crushing enough with my hand primer, but apparently I was not consistently getting them below the case head. Have now moved to a PCPS and all is well, but thought I'd share the little gadget I made to troubleshoot the issue.
This is a little shell holder sleeve that you can pop on the end of a set of Mitutoyo sized calipers and then use its depth gauge for reliable/consistent reference measurements. The way it works is you put a known-good (i.e. perfectly level with case head) primed case in the shell holder. Set your depth gauge zero off of that, and now you can make reference measurements on pocket depths and primer seating depths.
You can 3D print your own with: https://terminalcurves.com/downloads/primer-measure-sleeve.3mf
EDIT 12/29/2024: added an M5x0.8 set screw hole for folks that want to tighten it in beyond the friction fit. The way I run the threads on a print is I heat the screw a bit and then just thread it in slowly and let it set. Run it back and forth a few times and it should work fine. You can also just run an M5x0.8 tap real quick of course. It only needs a tiny bit of grabbing tension, don't over torque or you'll misalign the sleeve onto the calipers.
Important tip for usage over time:
For the detail oriented people. The reason it's a thousandths more in this picture than it is in the video (0.118"), is because in the video I zero'd off of a Hornady factory round which has the primer 0.001" below the case head. I used that as a reference to measure the pockets on my Alpha brass which are 0.119" (from reference measurement). For this picture I made a perfectly level dummy round to use as a consistent zero/reference so have repeatability across future measurements, which is why the picture is a thousandths more.
I recommend you do the same, i.e., keep a set of perfectly seated reference dummy rounds that will serve as your zero references for future comparisons. Or, alternatively, make multiple cases with both perfect zero and reference desired seating depths to offset from.
Hope it's helpful to someone. I saw the tools out there that are several hundred dollars and thought that's a bit obscene for functionality that comes in a standard set of calipers.
EDIT: In this demo I show repeatability/consistency of measurement across sleeves. There's purposely some slack in the sleeve for the shell holder slightly float, this slack is then taken up by the tension of the tailstock against the case. Because your zero is set off of a reference case, variances in the sleeve or shell holder itself do not matter. Also note that this solution works for both large and small rifle primer pockets. In the repeatability demo my reference case primer is 0.001" below case head and my pocket depths should consistently measure 0.118".
I use a 0.001" shallow reference primer depth because I primarily use this gauge to ensure my primers are never proud enough to mess with headspace. So when seating primers, I went them all to be 0.000 or -0.001 at the most to the reference.
This is a little shell holder sleeve that you can pop on the end of a set of Mitutoyo sized calipers and then use its depth gauge for reliable/consistent reference measurements. The way it works is you put a known-good (i.e. perfectly level with case head) primed case in the shell holder. Set your depth gauge zero off of that, and now you can make reference measurements on pocket depths and primer seating depths.
You can 3D print your own with: https://terminalcurves.com/downloads/primer-measure-sleeve.3mf
EDIT 12/29/2024: added an M5x0.8 set screw hole for folks that want to tighten it in beyond the friction fit. The way I run the threads on a print is I heat the screw a bit and then just thread it in slowly and let it set. Run it back and forth a few times and it should work fine. You can also just run an M5x0.8 tap real quick of course. It only needs a tiny bit of grabbing tension, don't over torque or you'll misalign the sleeve onto the calipers.
Important tip for usage over time:
For the detail oriented people. The reason it's a thousandths more in this picture than it is in the video (0.118"), is because in the video I zero'd off of a Hornady factory round which has the primer 0.001" below the case head. I used that as a reference to measure the pockets on my Alpha brass which are 0.119" (from reference measurement). For this picture I made a perfectly level dummy round to use as a consistent zero/reference so have repeatability across future measurements, which is why the picture is a thousandths more.
I recommend you do the same, i.e., keep a set of perfectly seated reference dummy rounds that will serve as your zero references for future comparisons. Or, alternatively, make multiple cases with both perfect zero and reference desired seating depths to offset from.
Hope it's helpful to someone. I saw the tools out there that are several hundred dollars and thought that's a bit obscene for functionality that comes in a standard set of calipers.
EDIT: In this demo I show repeatability/consistency of measurement across sleeves. There's purposely some slack in the sleeve for the shell holder slightly float, this slack is then taken up by the tension of the tailstock against the case. Because your zero is set off of a reference case, variances in the sleeve or shell holder itself do not matter. Also note that this solution works for both large and small rifle primer pockets. In the repeatability demo my reference case primer is 0.001" below case head and my pocket depths should consistently measure 0.118".
I use a 0.001" shallow reference primer depth because I primarily use this gauge to ensure my primers are never proud enough to mess with headspace. So when seating primers, I went them all to be 0.000 or -0.001 at the most to the reference.
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