Measuring barrel slug that has odd number rifling

[Ray B]

If I measure a slug from a barrel that has even lands and grooves the land and/or groove has the same on the opposite, so a micrometer can measure from a groove to a groove and a land to a land of the opposite side of the slug. The problem is with odd number l&gs one side of the mic is on the land while opposite side is a groove.

So is there an accurate way to measure the diameter of the bore when it has off rifling and I don't have a way to measure the depth of the groove?

 

[xausa]

Roy Dunlap gives his method of measuring barrels with odd numbers of lands and grooves on page 207 of his book "Gunsmithing". Basically, you measure the diameter of the bore plus one land, then you turn the casting down until the lands are removed and measure the bore diameter, then subtract the bore diameter from the first measurement, which gives you the land height, then double the land height and add to the bore diameter.