Hi Emmett,

Try this... Feel free to send me $20.00

To measure a bullet or a slug from a barrel with an odd number of grooves and lands (such as 5 or 7), standard caliper or micrometer jaws cannot sit directly across from a groove-to-groove line.

Alternative Measuring Methods

• The Shim Stock Method: Wrap a strip of known-thickness thin shim stock (or aluminum foil/thin paper) tightly around the slug so it conforms to the surface grooves. Measure the total outer diameter with a micrometer, then subtract twice the thickness of the shim stock to find the true groove diameter.
• V-Anvil Micrometer: Use a specialized V-block or V-anvil micrometer designed explicitly to measure odd-fluted or odd-grooved cylindrical objects.
• Land-to-Groove Calculation (The Math Method): Measure the distance from a land on one side to a groove on the opposite side.
     • As discussed by shooters on the Smith & Wesson Forum, you take that measurement, subtract the known or estimated bore (land) diameter, multiply that difference by 2, and add the bore diameter back in to estimate the groove size.
• Cylinder Throat / Pass Test (Revolvers): For revolvers with an odd number of grooves (like 5-groove Ruger or S&W barrels), slug the bore and see if the slug passes through the cylinder throats with a light slip-fit to verify dimensional match.
• Shearing the Slug: Carefully spin or turn a soft lead slug inside the bore just enough to shear off the raised groove impressions, reducing it to a pure bore-diameter slug, then calculate groove depth by adding measured depths back to the base bore size.
From A. I.condorsc wrote on Oct 22^nd, 2026 at 7:13am:

'Outilmeter' ... or some such crazy Euro thing ...

I have a couple micrometers for multi flute cutters ... somewhere between 3 and 5 flutes ... 6 would obviously be the same as a 2 flute ...

I have a v-block somewhere in the shop for measuring 5 groove barrels.
I seem to remember it's 108 degrees, and with a little mathematics, a slug can be measured quite accurately.