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Friday, July 19, 2024

What is Bore and Caliber of a gun? Explained in easy words

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 What is Bore and Caliber of a gun?

Okay. I chose this topic because I have met people who have confusions about what “caliber” and “bore” are. Also, I was asked the same question in 14 SSB Allahabad and I wish I would have known all this at that time. I think this post will tell you all you need to know about both the things, and clear all your doubts.

So what exactly is Caliber?

Short answer:  Width of the bullet determines its caliber.

Long Answer: The caliber is the size of the bullet. It can be measured in milimeters as in 7.62x39mm would be 7.62 milimeters across (diameter) and 39 milimers tall (length). Bullets are also measured as inches to like a 5.56x45mm could also be called a .223 because it is .223 of an inch wide.

In inches, Caliber, as a standard of measure, is given in tenths of an inch. though for technical purposes, thousandths of an inch are also given.
an M1 Garand fires a bullet having a diameter of .308″
an AK-47 fires a bullet having a diameter of .311″
They are both referred to as being .30 caliber rifles.

So then what is “Bore”?

Short Answer: Bore, in weaponry, is the interior of the barrel of a gun or firearm.

Long Answer: In the medieval period, the inner diameter of a barrel was frequently referred to as the bore (or gauge) of the weapon, and different weapons were classified by their bore size. This designation still exists in the present day, when referring to shotguns (e.g. 8 bore, 10 bore, 12 gauge etc.) .While most other weapons are classed in mm. or inches (for instance, 9 mm., .45 caliber etc.).

In guns that have rifled barrels, e.g., rifles, pistols, machine guns, etc. .The diameter of the bore is termed the calibre.

The bore diameter of a .30-calibre rifle is 30/100 of an inch, and that of a .50-calibre weapon is 1/2 inch.

The diameter of the smaller circle (measured from the tops of the lands) is the Bore Diameter. It is the largest round thing you could pass through the barrel, without having to miss-shape it to make it fit.
The diameter of the larger circle (taken from the bottoms of the groves) is the Groove Diameter. This represents pretty much the largest thing you can pass through the barrel, and whatever you push through it, will be cut, or pressed into by the lands of the barrel sticking up, in its way. Bullets, for the most part, are this diameter.

So if you understand how the gun works, you could say that caliber of a bullet is slightly higher than the bore caliber. But for a normal person, you could use those interchangeably for simplicity.

The measurement of the bore in shotguns is expressed in terms of gauge. The gauge of a shotgun originally was expressed as the number of round lead balls of bore diameter necessary to make a total weight of one pound. Thus, if eight lead balls of bore diameter added up to one pound, the shotgun was designated an eight-gauge gun. The smaller the gauge number, therefore, the larger the bore. Gauge, however, later became standardized in terms of diameter and no longer relates directly to the original method of determination. Under this standardized system, a 12-gauge shotgun has a bore diameter of .729 inch.

5.56 vs 7.62

It is often asked that which one is better 5.56 or 7.62 and in which situations which one is preferred? Try to find out the answer. A little homework, you see….

If you have more questions/suggestions do leave it in the comments section.

Thank You for reading.

Further reading….

Y Answers

Read my other posts here:

Structure and formation of Indian Army

The story behind badluram ka badan

10 facts about the Indian Air Force

Central Armed Police Force


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BlogsWhat is Bore and Caliber of a gun? Explained in easy words
BlogsWhat is Bore and Caliber of a gun? Explained in easy words


  1. Bore of a weapon is much too different than the term calibre. While bore is used for Smooth barrels, the term calibre is used for “rifled” weapons (Small or even artillery).
    Now, bore may be defined as the size of a smooth barrel of a weapon in which equal number equal sized balls made out of one pound of lead would snugly fit and pass.
    Hence, you’ll see that a 12 bore shotgun is a smooth barrel and is much larger than rifled small weapons. There s more….

  2. Its given in yr article that calibre is the width of bullet where as bore is the dia of magazine through which bullet is ejected out. So obviously dia or size of calibre has to be lesser than bore , otherwise bullet would struck up

    But in article it is mentioned calibre gauge should be higher than bore. But how it could be is beyond my comprehension.

    Kindly explain.

    • when fired only the bullet is accelerated and the cartridge casing is ejected out . thats why the case is slightly larger in diameter compared to bullet . you have noticed in some rifle ammos the body of the bullet is thicker in dia towards the bottom (ak47 bullet )

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