how do you measure exact bore size?

[james 14]

I know you use a micrometer but how do you measure the inside diameter? I guess you have to take a mold of it somehow. Can you measure the outside diameter and subtract the wall thickness or would that not be a reliable measurement?

 

[squirrelhawker]

I know you use a micrometer but how do you measure the inside diameter? I guess you have to take a mold of it somehow. Can you measure the outside diameter and subtract the wall thickness or would that not be a reliable measurement?

Bore gauge & micrometer. Rifled barrels have a "bore" and a "groove"
dimension. Many 45's are .450" bore - .458" groove. I measure between the lands for the "groove" and on them for the "bore".

 

[flounder]

I use an oversize roundball and gently tap it with a hammer and block of wood to get it started down the bore. Once started it slides down easily and I push it out the breech. You now have your inside bore dimensions ready to measure with a calipers.
Art

 

[mcrik]

A telescopic gauge (with mics or calipers) is fairly cheap & effective.

mcrik