Bullet Comparators

[F. Guffey]

The datum line is on the case shoulder and the "bullet ogive" is the circular point where the tip radius meets the bearing surface.

Not true. Both the chamber and the case have a datum, in the beginning reloaders thought the datum was a line and was located by an arrow pointing at it because, beneath the arrow was printed 'datum line'. Then, as in the beginning' there was no line except on drawings of cases in Lee's book on modern reloading and SAAMI.

The datum has from the beginning been a round circle/hole only to those that think in multiple dimensions as in side, front and top. the datum is 'measured from'. Common datum diameters of round holes, .375" and .400". For a reloader that understands the concept of measured from can use .357" or .400" of they understand they are using a comparator and they are not comparing the measurements with SAAMI specifications.

In the old days I use wire gage plates, bolt diameter plates and drill index orginizers, as I have said, this stuff does not drive me to the curb.

datum based tools do not have lines, they have holes that are round, I make datums, I collect datums and on occasions I purchase datums.

F. Guffey

[Brian Pfleuger]

Originally Posted by F. Guffey

I make datums, I collect datums and on occasions I purchase datums.

You also fixate on esoteric minutia and babble without a purpose beyond what I can only assume is your intent to confuse and your own perception that it makes you sound more knowledgeable.

Yes, the datum "line" on a case shoulder is technically a circle. This is a concept so basic that a kindergartner understands it without clarification, unless of course the "clarification" comes from you, in which case no one understands it.

If you really wanted to help people understand, you would write in a coherent, concise way with information pertinent to the question at hand rather than rambling, irrelevant nonsense.

[F. Guffey]

Yes, the datum "line" on a case shoulder is technically a circle. This is a concept so basic that a kindergartner understands it without clarification, unless of course the "clarification" comes from you, in which case no one understands it.

There is no line on the case, the measure from is a plane located by the round hole. Some like to make the round hole case friendly by using a radius at the edge, the radius changes the measure from/plane/flat surface.

The datum line is on the case shoulder

Yes, the datum "line" on a case shoulder is technically a circle. This is a concept so basic that a kindergartner understands it without clarification, unless of course the "clarification" comes from you, in which case no one understands it.

I said it was a round hole, there are some that believe it is located half way between the shoulder case body juncture and the shoulder neck juncture. How can that be? The 25/06, 270 Winchester, 280 Remington and the 30/06 have the same datum. They use the same 3/8" diameter hole. In thousandths that is .357".

When reloaders get to the point they can sort head space gages from comparators the diameter of the datum becomes a choice.

Add: As long as they use the same diameter hole, unless you have fond a way to move the line from one case to another.

F. Guffey