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Discussion Starter · #1 ·
Not sure if this is in the right forum but here goes: I have a 12 ga. shotgun with a smoothbore barrel and would like to measure the diameter at the business end. It is labeled as a full choke and the charts I've seen shows it should be right around .699". The upper jaws on the caliper I have are flat. Is there any way to estimate what the round bore would be using a flat jaw caliper?
What I'm doing is not rocket surgery, so I only need an approximation. I also don't wanna spend a bunch of dinero for a caliper I will use once. And no, I'm not gonna go out and buy one only to return it later. :D


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Is it just an outside caliper or a combo? Flat end or knife end?


If it has knife ends (like above) measure the OD then measure the thickness. ID= OD- 2 x thickness.
 

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I've always went by, if a dime won't fit in the muzzle of a 12gage, it's a full choke.
 

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Discussion Starter · #6 ·
I've always went by, if a dime won't fit in the muzzle of a 12gage, it's a full choke.
It is a full choke. I'm gonna have it opened up to an improved cylinder.

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Discussion Starter · #7 ·
Is it just an outside caliper or a combo? Flat end or knife end?


If it has knife ends (like above) measure the OD then measure the thickness. ID= OD- 2 x thickness.
Mine looks like that, but I didn't know they were called knife ends.

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How do you measure modified, improved cylinder & cylinder?
I'm going to have to get a little more technical to answer that.

I break out my readin specs, and read the writin what's writ on the barrel or screw in choke.
 

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Discussion Starter · #10 ·
The top Knives are inside diameter
I realize that and I use the "top knives" for measuring inside flat surfaces. There are calipers available that are radiused for use on inside round surfaces. I can get a relatively close measurement with what I have.

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Discussion Starter · #11 ·
I'm going to have to get a little more technical to answer that.

I break out my readin specs, and read the writin what's writ on the barrel or screw in choke.
I like your reply. If I wanna know what type of choke the gun has I just read it on the barrel.

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Get a Lincoln Memorial penny (12 Ga.) if the base matches Modified; if it sinks the the first step around IC.

Better yet shoot a quality #8 at a 30" circle at 40 yds. 350 pellets to the ounce. Over 70% is full. You can find the other numbers on the net. Performance beats coins, calipers etc.
 

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I realize that and I use the "top knives" for measuring inside flat surfaces. There are calipers available that are radiused for use on inside round surfaces. I can get a relatively close measurement with what I have.

Sent from my Commodore 64 running Windoze 95
You do realize that you can use the top knives to measure inside diameters? Just insert into the bore and extend. They're self centering
Done!
 

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Discussion Starter · #14 ·
Get a Lincoln Memorial penny (12 Ga.) if the base matches Modified; if it sinks the the first step around IC.

Better yet shoot a quality #8 at a 30" circle at 40 yds. 350 pellets to the ounce. Over 70% is full. You can find the other numbers on the net. Performance beats coins, calipers etc.
I've used various coin tricks in the past. I also found some 4-1-1 on the Internet regarding shot patterns, pellet sizes, distances, percentages, etc.

Sent from my Commodore 64 running Windoze 95
 
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