I have just finished searching the Reloading section re the Davidson Bullet Seating Checker for an answer to a possible problem.

I have been using the Stoney Point comparator for some time but thought the Davidson set up with the base would be better.

Used the Davidson for the first time today and found the resultant measurement was very different to the Stoney Point. For example when measuring with the Stoney the reading was 1.911". Measure the same cartridge with the Davidson and the reading was 1.8 something. I've measured the inside diameter of the nose for both the Stoney and the Davidison as best I can and they appear to be the same.

What's going on or what am I doing wrong?

They are both "Comparators" and are used to compare YOUR handloads to your needs and specs.
As they are "Comparators" they will be slightly different and are not made to "Compare" to each other. Pick one and use it, do not expect measurements from one "Comparator" to another to be the same.

Thanks for the reply

quote:

I've measured the inside diameter of the nose for both the Stoney and the Davidison as best I can and they appear to be the same.

“I've measured the inside diameter of the nose for both the Stoney and the Davidison as best I can and they appear to be the same.”

There is a concept called ZERO. if the tool used to measure ‘from’ is closed and zeroed the tool is not a comparator, a comparator measurer the difference between two lengths, something like before and again after.

Datum: measure from, the datum for the 30/06 family of cartridges is .375, when determining the length of a case from the shoulder/datum to the head of the case the shape of the datum effects the length by changing the ‘measured from’.

If the datum is a straight round hole that is cut 90 degree to the plane, the plane is the ‘measured from’. If the .375 hole has a radius the .375 datum will be below the plane. Meaning? There is no way to zero the tool.

The Wilson case gage is a very precision tool, it is a datum based tool, meaning the case when placed in the Wilson case gage the case sits on a datum that is a radius.

Back when I thought reloaders were very capable of making tools I suggested drilling holes like the .375 diameter hole used with the 30/06. Instead of drilling holes they went to Home Depot and purchased bushings with 3/8 diameter holes then went off proclaiming they had invented something. I felt obligated to caution them about the accuracy of a datum with a radius.

F. Guffey

Mr Guffey has it right, but I'd guess the difference is the depth of the base piece, assuming that the other dimensions of the nose pieces are the same. You can't "zero" at true zero unless the nose piece can be made to go right up against the base without butting against the shoulder of the base first. I know what the Davidson looks like, but without having one I can't tell exactly. Either way, it's just a tool to measure relative to other measurements taken with the same tool as Mr Guffey said.