Caption: Plug gauges
are used to measure revolver chamber mouths.
All measurements can be taken with automotive-type spark plug gauges
or similar with the cylinder closed.
While on the subject of measuring tools, to check cylinder chamber mouths I bought a set of plug gauges
from machine a tool supply outfit called ENCO.
Cerulean and Micro-Epsilon are examining other potential applications for the instrument including measuring the dimensions of wires, rods, plug gauges
A set of plug gauges
showed the 4" version had .358" chamber mouths; a .359" plug would fit in none of the six.
Now I keep a record of the chamber throats (much easier to measure using plug gauges
) and size bullets accordingly.
Several years ago I purchased a set of steel plug gauges
measuring from .250" to .500" in increments of .001" and they have turned out to be one of the most important tools on my reloading bench.