Possibly dumb question about datum planes

[Urbanti]

So I am setting up my reloading table to reload .220 Beggs.

Part of that process involves measuring the headspace of both fired and sized cases using a Hornady comparator attached to a digital caliper.

To use the comparator you need to attach the correct comparator headspace insert into the tool, inserts come in .330”; .350”, and .375” for instance.

Usually to accomplish this I refer to reamer prints for the case in question to determine where the datum line is located on the case and thus which Hornady comparator insert I should use.

Looking at several reamer prints, it looks like some depict a .330” datum plane, and others depict a .375” datum plane, thereby leaving me confused as to which Hornady headspace insert to use in the comparator, or whether it makes a difference so long as you always use the same one?

Maybe I’m misreading the reamer prints.

Thanks in advance for any insights!

Tim

 

[zippy06]

There are a few versions of the 220 Beggs. That is prolly the problem. Gotta go with what's real. What comes out of your chamber.
I had a very early version. Got it all from a friend. Took almost a year to get a barrel. I think 2nd shortage.
You can use the old way. Empty case into chamber. Strip bolt. Size until bolt handle falls 1/2 way. That's really the best way.
No numbers. Minimize the moving parts. And you know it's gonna fit.

 

[rsmithsr]

my answer would be, gene only changed the neck shoulder radius..so if cip has a drawing, what ever they say for 220 russ

 

[zippy06]

my answer would be, gene only changed the neck shoulder radius..so if cip has a drawing, what ever they say for 220 russ

oh. I talked to him back then. I think, he said there were 4 versions. He asked about my reamer. What number? I told him there was no number.
He said oh and talked about something else. Sounded like version 0 or 1. I remember I had to turn necks. I seem to remember other versions were no turn necks. I made a bunch of 52gn 7 ogive FB. 14 twist. Shot it for a summer.