mm to caliber conversion chart

[mred]

Some of the numbers don't look right but close. Such as 9mm=.354 when a 380 cal. is called a 9mm short and like 5.56mm=.225. What part am I missing? Thanks.

[seamusTX]

Most calibers are nominal. The actual bullet diameter is slightly different. For example, .38 Special and .357 Magnum are exactly the same diameter.

I don't think you can have a simple chart because of all the variations. There are often five or more different variations on a nominal caliber (for example, 9 mm Luger, Kurz, Largo, 9X18, etc.)

If you go to ammoguide.com and register, you can call up the exact dimensions of the bullet and case of any round.

This site sends e-mail maybe four times a year. It's not a spam generator.

- Jim

[Crossfire]

What you are missing is that you thought there was some standard naming convention for calibers. Sorry, no such logic exists in the ammo world. Pistol is bad enough. Rifle calibers are worse.

[WildBill]

Most calibers are nominal. The actual bullet diameter is slightly different. For example, .38 Special and .357 Magnum are exactly the same diameter. - Jim

And some of it is marketing. The .44 Magnum has a .429" diameter bullet. Somehow .43 Magnum doesn't sound as good.

[mred]

Yes, I guess I had a thought and I guess you cleared the question up for me, sorry.

[seamusTX]

There's nothing to be sorry for. The world of firearms has all kinds of weird inconsistencies (just like the rest of life). Nobody is born knowing them.

- Jim

[C-dub]

Just like clothing. Some 34" waist pants fit loose and some fit tight. Measure them and it'll drive you nuts.

Kind of like a 2x4 piece of wood isn't 2" x 4".

[seamusTX]

And what about "penny" nails? Why isn't a 4-penny nail twice as long as a 2-penny nail?

The penny size was originally the price in [16th-century British] pennies of 100 nails of that size. The hundred was the great hundred, 120, not 100.

http://www.sizes.com/units/penny.htm" onclick="window.open(this.href);return false;

Let's not even get started with shot sizes.

- Jim

[WildBill]

And what about "penny" nails? Why isn't a 4-penny nail twice as long as a 2-penny nail?

The penny size was originally the price in [16th-century British] pennies of 100 nails of that size. The hundred was the great hundred, 120, not 100.

http://www.sizes.com/units/penny.htm" onclick="window.open(this.href);return false;

Let's not even get started with shot sizes. - Jim

At least shotgun gauges make some sense.

[srothstein]

At least shotgun gauges make some sense.

You mean like a 20 gauge is larger than a 12 gauge and a 410 gauge is humongous, right?

[WildBill]

At least shotgun gauges make some sense.

You mean like a 20 gauge is larger than a 12 gauge and a 410 gauge is humongous, right?

That's exactly what I meant.

[mred]

Nominal sounds right to me so now I know. Thanks Seamus for your reply.

[mr surveyor]

...except that .410 is a caliber instead of a gauge.... now what about those railroad gauges

surv

[ScottDLS]

Just to be fair, an inch is defined as EXACTLY 25.4mm and the physicists have defined the meter (1000mm) as the length of the path traveled by light in vacuum during a time interval of 1⁄299 792 458 of a second. Speed of light (in a vacuum) being an absolute constant of the universe, kinda like pi.... Well you get the idea.

Anyway bullet calibers while nominally supposed to be measured in inches don't seem to be exactly reflective of their actual diameter. Seems the (original) gun manufacturer gets to determine the exact specification, then name the ammo as some approximation that sounds cool. Thus the .43 inch .44 magnum, the (roughly) .357 inch, 38 special. Maybe that's why it's special.

Also bullet diameter doesn't necessarily have anything to do with cartridge/chamber size. Hence a 7.62mm X 39 AK round not working too well in a NATO 7.62x54 gun (aka .308 cal).

I do seem to be able to shoot .22 cal LR out of my Ruger 5.56mm NATO (nominally .223 cal) pretty well, but only after putting a Ciener .22 cal conversion bolt kit in. Sounds like an angry bee in full auto vs. a jackhammer with the 5.56 NATO.

I heard in Mexico they make a (nominally) .222 cal version of the AR15 because private individuals are not allowed to own guns in Mexican military calibers. This .222 won't fire 5.56mm NATO/ .223 cal ammo, so it meets legal requirements. I suspect the .222 cartridge might be shaped differently too, on purpose so it won't work in military guns.

[Mike1951]

50+ years ago, the .222 Remington and .222 Remington Magnum were extremely popular here and served as the basis for the .223.

The popularity of the .223 caused the decline of the .222's.