Re: Hornady LNL OAL gauge question
The context of ogive is often assumed as the point where lands would first contact a bullet nose. That's the datum desired.
But a bullet ogive is not a datum point. 'Ogive' is really a term to define the curve of a bullet nose, rather than a specific place on that curve.
That desired datum(first contact) varies with angles, both related to the nose curve, and the bore leade angle. And while a datum can be calculated, your tool will not match it.
The only matching tool that I know of is a barrel stub throated with the same reamer used to cut your chamber('gizzy').
Without this, you still have a relative datum provided by your tool. It is simulating land contact.
But no matter the tool, the datum provided will change with each different nose curve, cuz different nose curves actually do contact lands differently.
Same lands(simulated or not), but tangent ogive curves(SMK) are way different than secant ogive curves(VLD), so the datum moves.
All that matters is that you determine ogvOAL for EACH bullet type you intend to use & log it.
Focus on reproducing these lengths based your measurements, with your tool.
Hell, I use is a Sinclair 'nut' (nothing fancy). But as long as I can reproduce the exact seated measure with that tool, I'm good to go.