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Conversion Confusion 5.56 mm/.223 in

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Richard Huelbig

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Jun 5, 2000, 3:00:00 AM6/5/00
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I know that a 5.56 mm bullet is supposed to be the same as a .223 inch
bullet. Why then do the conversions come out wrong? If I convert 5.56 mm
into inches, the result is .219", not .223". And, conversly, when I convert
..223 inches into millimeters, the result is 5.66 mm, not 5.56 mm. I'm using
the conversion factor of 1 inch = 25.4 mm.

These two types of ammunition are 100% interchangeable, are they not? Also,
why the differences when I do the conversions?

Thanks,

Richard Huelbig


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Smokin Joe

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Jun 5, 2000, 3:00:00 AM6/5/00
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5.56 is the BORE diameter, not the groove diameter

Richard Huelbig wrote:
> ...

stoatman

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Jun 5, 2000, 3:00:00 AM6/5/00
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Because the figures quoted are not nominal, e.g. .303" is nominally .311
(7.7mm) and 7.62mm is nominally .308" (go figure).

Don't worry about nominal diameters, just buy the right bullet for your
calibre.

Peter Torvik

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Jun 5, 2000, 3:00:00 AM6/5/00
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#I know that a 5.56 mm bullet is supposed to be the same as a .223 inch
#bullet. Why then do the conversions come out wrong?

One is the bullet diameter diameter (typically, the same as the groove
diameter) , the other is the land diameter. The same thing happens in .30
caliber. The 7.62mm is the land diameter, and converts to .3 in. But the
bullet diameter is .308 inches. Thus, the bullet diameter of the 7.62 NATO
is the same as the .308 Winchester. (Note to other readers: Please note I
didn't say ANYTHING about whether or not the rest of the cartridge or the
chamber or the pressure is or is not the same!)

Peter Torvik

Edward Arnold

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Jun 5, 2000, 3:00:00 AM6/5/00
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And if you _really_ want to be confused, try converting "7.62mm" to U.S.
measure. Comes out 0.29999 inches on my calculator, which of course is the
clue: the metric folks chose to indicate the bore dimensions, not the groove
diameter or bullet diameter. Which is where we get the .30 caliber "7.87mm
Lazzeroni", etc.

Ed Arnold
----------
#From: "Richard Huelbig" <huel...@bellatlantic.net>
In article <8hg9mg$9db$1...@xring.cs.umd.edu>, "Richard Huelbig"
<huel...@bellatlantic.net> wrote:


#I know that a 5.56 mm bullet is supposed to be the same as a .223 inch

#bullet. Why then do the conversions come out wrong? If I convert 5.56 mm
#into inches, the result is .219", not .223". And, conversly, when I convert
#..223 inches into millimeters, the result is 5.66 mm, not 5.56 mm. I'm using
#the conversion factor of 1 inch = 25.4 mm.

hamrdog

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Jun 6, 2000, 3:00:00 AM6/6/00
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actually, to make it even more confusing, when you look for .223 cal
bullets, they're .224.

i guess it has to do with where the measurements are taken, the grooves
or the lands. but who knows how they come up with half this stuff.

andy b.

Lone_Wolf

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Jun 6, 2000, 3:00:00 AM6/6/00
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In <8hg9mg$9db$1...@xring.cs.umd.edu> "Richard Huelbig" <huel...@bellatlantic.net> writes:

#I know that a 5.56 mm bullet is supposed to be the same as a .223 inch
#bullet. Why then do the conversions come out wrong? If I convert 5.56 mm
#into inches, the result is .219", not .223". And, conversly, when I convert
#..223 inches into millimeters, the result is 5.66 mm, not 5.56 mm. I'm using
#the conversion factor of 1 inch = 25.4 mm.

The problem is that the conversion factor isn't precise enough. I don't
have one of my physics books handy to get the conversion factor to a more
precise number of significant figures (basically, you'r dealing with rounding
errors for part of the problem).

#These two types of ammunition are 100% interchangeable, are they not? Also,
#why the differences when I do the conversions?

Umm... not exactly... A rifle chambered for 5.56 NATO will usually have a
longer throat than one chambered for .223 Remington. Won't usually cause
problems, but every weird once in a while you'll have problems firing 5.56
ammo in .223 chambers.

James

... ...

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Jun 6, 2000, 3:00:00 AM6/6/00
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To add to the confusion , My Sierra reloading manual lists the .223
bullet as.224 diameter.
The nly thing I know for sure is that there are some strange things
when You look into caliber and what they mean .

Bill

Bill Boyanton

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Jun 12, 2000, 3:00:00 AM6/12/00
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To further add confusion... .223 Rifles shoot .224 size bullets....

They are the SAME thing. Don't worry
5.56mm IS .223
.223 IS 5.56mm

Sometime some rifles are measured from land to land other groove to groove,
hence the diff.

Don't sweat the small shit.

They are the same round.

misifus

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Jun 25, 2000, 3:00:00 AM6/25/00
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Lone_Wolf wrote:

# The problem is that the conversion factor isn't precise enough. I don't
# have one of my physics books handy to get the conversion factor to a more
# precise number of significant figures (basically, you'r dealing with rounding
# errors for part of the problem).
#

Actually, 25.4 mm = 1 in. is pretty accurate. To four significant digits, it's 25.40 mm =
1.000 in. The point is still that the measurements don't work out to be equal to the
ammunition naming conventions.


--
Ralph Seibert
guitar player and physics teacher
mis...@mesh.net
http://www.mesh.net/~pituso

Julius Chang

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Jun 25, 2000, 3:00:00 AM6/25/00
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misifus wrote in message <8j50in$663$1...@xring.cs.umd.edu>...
#Actually, 25.4 mm = 1 in. is pretty accurate. To four significant digits,

it's 25.40 mm =
#1.000 in. The point is still that the measurements don't work out to be
equal to the
#ammunition naming conventions.
#
#
#--
#Ralph Seibert
#guitar player and physics teacher

That trailing zero in 25.40 is not a significant figure.

Physics teacher?

Julius


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vZc

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Jun 25, 2000, 3:00:00 AM6/25/00
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5.56/25.40 = .2188" which a nominal bore land diameter for SAAMI spec REM
223 bullets which are .2240" diameter [URL].

http://www.hornady.com/html2/matchart.html#anchor190660

Allan Howard

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Jul 8, 2000, 3:00:00 AM7/8/00
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# Actually, 25.4 mm = 1 in. is pretty accurate. To four significant digits,
# it's 25.40 mm = 1.000 in.

#> That trailing zero in 25.40 is not a significant figure.

Yes, actually it is. 1 inch has been _defined_ to be EXACTLY 25.4 mm.
That's to an infinite number of significant digits. This is a world wide
accepted definition for length conversions.

Allan Howard
Mechanical Engineer

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