I'm making my own comparator set. What are the diameters that Stoney Point uses? I'm thinking .005" smaller than bore since most lands (I think) are .005" high. That would usually split the difference.

.224 use .219
.243 use .238
.257 use .252
.264 use .259
.277 use .272
.284 use .279
.308 use .303
.338 use .333
.358 use .353

Are these correct? Anything popular in between missed?

Hello PEI Rob,

Those diameters should work, all you are using them for is comparison. As long as you're under bullet diameter you will stop the gage before the bullet slides through. I have never tried Stony point/Sinclair, etc. gages, so I can't tell you what diameters they use.

I think grooves in typical medium bore barrels are actually around 0.004" deep, meaning that the "bore" diameter would be .256" on a .264" (6.5mm) groove diameter barrel, for example. They might be shallower in smaller or deeper in larger bore barrels.

Regards, Bill

PEI ROB
New Member
Member # 9813
posted 11-21-2002 01:45

quote:

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I'm making my own comparator set. What are the diameters that Stoney Point uses? I'm thinking .005" smaller than bore since most lands (I think) are .005" high.

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Ooops, if lands are .005, that would be .010 " since two lands are involved� if they are opposite each other. It is likely they are not since the land count typically exceeds 2 (or 4).

Then you are into trigonometry to figure the land height(s) and their consequential reduction(s) to make the comp[arator.

Buy a Sinclair "nut" and save the energy. And yes I know "home projects" have a sense of satisfaction that doesn't come from "store bought" but you are re-inventing the wheel, IMHO.

A .224" diameter bullet.
0.005" lands, pretend there is an even number of opposed lands for us mathematically challenged folks
Land diameter .214"
Split the difference .219"
Use this as a reference point that will touch the lands but not the bore. This is where the complicated math loses its importance.
This is how the OAL gauge is determined correct?
Its the comparator I was wondering about.
Measuring COL at .214" rather than at the tip will be MUCH more accurate in determining distance to lands because of variations in shape in any lot of bullets.

Maybe I should use 15 thou under?

For $50 CDN by the time it gets here I think I can use some 1 inch 1/2 X 20 bolts, true the face and bore and poilsh some holes. Screw one of these home onto a long nut with a small bolt and slot cut into it and presto, one homemade tool kit you can be proud of.

Sysephus your right, Dooouuuhh This is why I was asking though. And we both know it would be a lot easier but I'm "highly focused" at the moment

[ 11-23-2002, 04:05: Message edited by: PEI ROB ]

Hey Rob, I've got one of the Sinclair Comparitors and it is a nice tool. But, I've had just as good a luck going to a tool box with Standard and Metric "sockets" and using one of them for a Comparitor.

I'd recommend you simply use the largest drilled hole that will not slip past the Ogive for each caliber. Nothing tricky or complex is needed for the Comparitors you make to work properly. Just be sure to use the "same one" each time for a specific caliber.

Good luck to you.