Measuring the barrel ID
I’m not a machinist or even have plans on doing any modifications. I’m just curious.
Say you have a choked barrel in .22 but you want to know how many thousandths it actually is. How do you do this? I know you use a micrometer for measuring in thous but obviously you can’t here.
Once again, my curiosity sends me on an all day chase. 😀
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Well……
Now you know the rest of the story. 😛
Welcome aboard the forum BTW.
RC
Again, I’m not interested in doing this. I was interested in how it was done because I was curious.
I slug barrels quite often, because I shoot cast bullets in air gun barrels and thus you have to know the exact groove diameter to get the best accuracy.
Groove diameter is the meausurement of the lead displaced by and into the area removed from the bore by cutting the rifling. Bore diameter is the measurement of the barrel before the rifling was cut.
You can do it with a pellet, by squeezing it down, but there are better ways.
I think Brownells still sells slugs for this exact prupose, but if I were you this is what I would do, find a 22 rimfire catridge. REMOVE the bullet from the case with a pair of pliars. The reason I capitalized REMOVE is because if youtry to tap in a live round in your barrel you will loose a finger or an eye.
The removed slug will be slightly oversize, but that is what you want.
If your gun is an airforce rifle, remove the tank, if it is another brand, you will need to remove the barrel because you have to start the bullet in the breech and push it down the bore with a cleaning rod.
Now you will need to lube that bullet with a good oil to reduce friction. And you will need a stout cleaning rod and a brass hammer and a brass punch to start the bullet into your barrel.
Tap the oiled bullet your REMOVED from the case into the breech gently until flush with the brass hammer, then with a brass punch that is smaller than the interior of your barrel, carefully tap the bullet into the barrel about 1/4 inch and no more.
Now push the bullet only halfway down the barrel with the cleaning rod.
The reason is you have to push the bullet halfway down the bore the first time and then back out the breech, is because this is going to give you the groove diameter of the barrel without the choke interferring with your measurement.
Now you can mearsure the slug, you pushed halfway down the barrel and then back out the breech, at its widest point to get the groove diameter without the choke.
To measure the choke, push the bullet down the barrel again except this time push it all the way out the muzzle, and this wil give you the measurement of the groove diameter of your choke.
I hoope this helps,
Regards,
Roachcreek
Makes sense to me. Thanks!
Not sure, but I believe you slug the barrel, with a pellet, and then carefully measure the pellet’s OD.
Use a wood rod and drive a lead slug through the barrel. Use a clutch type micrometer to measure slug’s OD. Non clutch micrometer’s will not give an accurate measurement because they will compress or deform the soft lead.
Sam 
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Usually use Cerrosafe to check chamber diameter. (you can Google it) It is a metal alloy that melts at about 160 degrees. You lightly oil the barrel, and plug it just ahead of the chamber with a cleaning patch. Not too tight. You pour the melted Cerrosafe right in the chamber, using a tube if needed. It cools very fast and can be tapped out. It shrinks just as it sets, but in one hour is EXACTLY the diameter of the chamber. It is also good for seeing if the chamber has any errors in machining.
That is how it is usually done in the gunsmith community.