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How to Measure a 5-Groove Barrel

Military-surplus rifle enthusiasts tend to use home-cast lead bullets to save money. Because rifle bore diameter can vary substantially from one rifle to another, it is often a good idea to drive a soft lead slug into the barrel to make an impression of the rifling. The rifleman then measures the outside diameter of the slug and chooses a bullet diameter that is .001 to .002 inches larger than the slug. This technique works well if the rifling in the barrel consists of an even number of grooves. 5-groove barrels are common, however, and these require a different measuring tool.

Things You'll Need

Rifle cleaning kit with one-piece rod
Lead "egg" fishing weight assortment
Leather mallet
V-anvil micrometer

Instructions

- 1
  Unload the rifle.
- 2
  Clean the bore of the rifle. Use a patch to lightly oil the bore.
- 3
  Set the butt of the rifle on the floor. Set an egg sinker on the muzzle of the rifle. The correct size sinker will be too large to push into the bore by thumb pressure alone.
- 4
  Use the leather mallet to drive the sinker into the barrel. Drive the sinker through the barrel and out the chamber end with the cleaning rod.
- 5
  Set the sinker into the micrometer so two groove impressions (larger-diameter sections) of the sinker contact the V-anvil. Close the micrometer so its spindle contacts a third groove impression.
- 6
  Read the indicated diameter on the micrometer scale.

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