Re: How accurate should COL be?
The term 'ogive', relates only to the curve of a bullet nose. That is, the curve type and amount, expressed in cals of radius.
It is NOT a datum on a bullet nose.
Shooters assume that the 'begining' of a bullet nose section, or 'end of bearing', equals the ogive and the point where first contact is made with the barrel leade. But this is not an established datum(a standard). Nobody official has has declared that OgvOAL equals casehead to 1thou under cal, or 5thou, or 20thou. In fact, I just made up the term OgvOAL, without qualifying it at all...
Also, the first contact point to leade is completely dependent on leade angle-vs-ogive shape. And there is no standard w/resp to datum in either seater plugs or OAL comparators.
It's all realative.
BUT, there are trends with reason.
Comparators generally take a datum near cal diameter, but not so close as to cause inconsistent readings from varying measure pressure.
Seater plugs contact quite a bit further down the nose, and with greater contact area, because there is way more pressure applied in bullet seating. So higher gripping angles are called for -to push against. But if you excessively size necks there can still result enough seating force to damage bullet noses, and cause variances in seating depth.
I for one am glad seater plugs are just the way they are, and I'm sure this was the result of trial & error testing by die makers. If the seater plug contacts too high on a bullet nose, especially a tangent ogive nose, the contact angles become so shallow that consistent seating would be impossible without very low seating forces(about as much force as we measure OgvOAL with).
A seater plug can be lapped for better seating, but with atleast as much contact lower on the noses.
I do wish there was a standard datum that all comparators and seating plugs were then based on..
siegrisj, when you make ammo you should have no problem getting far better numbers than those Federals.