I have merged two threads that had basic shotgun data in them into this thread. If it reads a little "funny", that's why.

Here's a handy equation I found for calculating the bore diameter of given shotgun gauge.
 
Bore diameter = 1.66992 X 1 / gauge^0.333
 
In words: The bore diameter in inches is equal to 1.66992 times one divided by the cube root of the gauge.
 
For example, what's the bore diameter of a 24 gauge shotgun?
 
"caliber" = 1.66992 X 1/2.8845 = 1.66992 X 0.34668 = 0.579"
 
2.8845 x 2.8845 x 2.8845 = 24 - Therefore 2.8845 is the cube root of 24.
Using this equation for the 12 gauge yields a bore diameter of 0.729".

Works for me.

Paul

A bit easier than figuring how many lead balls of the bore diameter are in a pound.        12 balls = 12 gauge, 20 balls=20 gauge, ect...

Egzackly...
 
Paul

Gettting tired of trying to find what the "caliber" was for a given shotgun gauge, I decided to put a table of such in with my other ballistic calculation spreadsheets. There is a nice formula for converting gauge to caliber (in inches), and having done it for the "normal" gauges - 10 to 32 - I decided to 'run it out' in both directions. So I did - from 1 ga to 911 ga. Why 911 you ask? 'Cause that's where the caliber is .172", the smallest commercially available projecitles. Hmm...
 
I decided to make sure the calculations were consistent with what tradition says "gauge" meant, which was the number of balls of the specific diameter in a pound. In expample, there are 16 pure lead balls of 0.662" diameter a pound. There are 12 such balls of 12 ga diameter, etc. Fortunately for me, the numbers came out right.
 
Then, after looking at the "small" gauges,I decided to make a table that had the number of pellets of a given "gauge" or caliber per ounce. This for determining about how many pellets of a given "gauge" would be in a 1 oz. charge for a shotgun. Since the diameters of the common pellet sizes are known, I could once again check my calculations against the know numbers. Again, miracle of miracles, the numbers "checked out". Then I noticed something...
 
Mathematically speaking, integers (whole numbers like 1, 2, 3...) are "interesting" when they show up among a bunch of "real numbers". ("Real numbers", mathematically speaking are those numbers with decimal points like 1.2, or 5.7, or 15.346...) When I looked at the caliber where and integer number of pellets/ounce occurred, I saw an interesting pattern. Have a look at the attached image.
 
In a nutshell, where there occurred an integer number of pellets per ounce, the caliber associated with that "gauge" was, for the most part, a common caliber. I'm always looking for an explanation as to why some "standard" was established. In the case of firearms history, there are precious few answers to "why" questions. Here may be some brief glimpse through the haze of history that had something to do why someone chose for example, .258 as a caliber.
 
Paul
 
The original thread in its entirety can be found here:
http://www.thehunterslife.com/forums/showthread.php?t=13499&highlight=Interesting
 
You are encouraged to read it.
 
Paul

For future reference, if you want the bore diameter of a particular shotgun gauge, the following formula will get you within a thosandths of nominal:
 
Caliber = 1.66992 * the cube root of (1/gauge)
 
If your caculator won't do cube roots, but will raise "x" to a "power", the equation becomes:
 
Bore = 1.66992 * (1/gauge) raised to the 0.33333 power.
 
Paul

A couple of things...

First - "Bore" has a specific definition: The number of solid lead balls of the specific diameter that equal one pound in weight.

Second - Anyone that makes a shotgun could make the diameter of the barrel equal anything they wanted and call it anything they wanted. This is actually quite common. The naming of the chambering is more important than a few thousandths here or there in bore diameter.

Third - Shotguns aren't rifles - meaning that bore diameter isn't as critical in a shotgun as it is in a rifle.

Fourth - The diameter of the bore at the muzzle is NOT the "bore diameter" of a shotgun unless it is choked "cylinder". Even then, there is sometimes some constriction.

Fifth - I didn't start this thread so one could calculate the "bore" of a shotgun to the 0.001". If it's that important to you, it should measured, not estimated. (However, measuring a shotgun's bore isn't trivial. One needs a special tool to reach far enough into the barrel to pass the choke at the muzzle or the forcing cone at the breech.) I started this thread so that a person could get an idea of what the BORE - not choke - of a shotgun with a particular NAMED chamber would likely be, based on the definition of the term "bore" as it relates to shotgun barrels.

This is a reference thread for those that might want to know the nominal diameter of their shotgun's bore, or wanted to calculate the bore of an "odd-ball" shotgun they own, or calculate the "gauge" of an old smoothbore rifle.

Paul

I thought this would be a good place to put a "shot size" chart.

Paul

Might as well 'do the math'...

Paul

I decided just to put all of the shotgun related data in this thread.

Average Pellet Count Per Ounce


For "HeavyShot"


Ballistically "Equivalent" shot types


Paul