I have a set of telescoping hole gauges, and can say from experience that you won't get a true reading of bore diameter using these gauges when measuring a rifled bore. One side may be resting on top of a land, and the other side might be resting on the edges of TWO lands, but not reaching the bottom of the groove.
These telescoping gauges work pretty well on smoothbores though.
There is another type of small hole gauge with an expanding round ball, or expanding cylindrical measuring surface that will give a true reading to the top of the lands.
One example of this type of small hole gauge is at this URL;
[url] http://toolsolutions.zoovy.com/product/728-532?META=froogle-728-532[/url]
A search on "small hole gauges" should turn up more information.
However, I think we try to overthink things like this. Knowing the true bore diameter will not solve the problem of what ball diameter, what patch lube, or which patch thickness will give the best accuracy in a specific gun.
The best way to find the optimum load is to get several ball diameters, a few thicknesses of fabric, and a good graduated powder measure and go to the range.
If your gun is 20ga (62 cal), chances are 99.99 % that the bore diameter will be .620, plus or minus a thousanths, or two. That means measuring true bore diamter is a mute point, and in the long run won't make a nickels worth of difference. You still have to experiment with several patch/ball/powder combinations to get the best accuracy.
It would help if we knew what you are shooting, and what ball dia/patch/powder charge you are using.
J.D.
These telescoping gauges work pretty well on smoothbores though.
There is another type of small hole gauge with an expanding round ball, or expanding cylindrical measuring surface that will give a true reading to the top of the lands.
One example of this type of small hole gauge is at this URL;
[url] http://toolsolutions.zoovy.com/product/728-532?META=froogle-728-532[/url]
A search on "small hole gauges" should turn up more information.
However, I think we try to overthink things like this. Knowing the true bore diameter will not solve the problem of what ball diameter, what patch lube, or which patch thickness will give the best accuracy in a specific gun.
The best way to find the optimum load is to get several ball diameters, a few thicknesses of fabric, and a good graduated powder measure and go to the range.
If your gun is 20ga (62 cal), chances are 99.99 % that the bore diameter will be .620, plus or minus a thousanths, or two. That means measuring true bore diamter is a mute point, and in the long run won't make a nickels worth of difference. You still have to experiment with several patch/ball/powder combinations to get the best accuracy.
It would help if we knew what you are shooting, and what ball dia/patch/powder charge you are using.
J.D.
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