Parker 12ga bore diam.

[Bill Murphy]

I also use a "skeets" type micrometer that I bought from Galazan years ago. I also have a great instrument sold by Galazan that measures 10 to 28 and sells for more than $400. I don't know if this one is still in Tony's catalog or not. It works without any springs and is very accurate.

[Double Lab]

I've got the Galazan gauge and find it is accurate enough but it won't fit into the muzzles of my 28 Parkers or my Pieper 28. Those I use the Bore Master which once you learn to use it is accurate enough.

[mobirdhunter]

I checked my record log which has bore diameter listed. My gauge is the one sold by Brownell's. I'm listing the date of manufacture for that reference.

.754/.754 1884
.753/.753 1886
.751/.756 1889
.761/.762 1889
.752/.751 1890
.753/.753 1891
.753/,753 1893
.734/.736 1896
.735/.734 1904
.732/.732 1912
.733/.731 1923

A small sample size, but it is suggestive. All of these guns measure with sufficient wall thickness (in my estimation and based on advice gotten from members here), and all have been shot numerous times.