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Old 04-09-2012, 09:56 AM
NETWizz NETWizz is offline
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Default Caliber to mm Conversion.



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Well as most of you figured out, mm is metric for millimeter. In fact, it almost insults your intelligence to bring it up.

A 9mm bullet is 9mm, which is .9 cm

In contrast, caliber is hundredths of inches, so a 1 caliber bullet would be 1/100th of an inch.

A 50 caliber bullet would be 50/100ths or 1/2" in diameter.
************************************************

2.54 cm per inch is the conversion from metric to standard.

It can be said that a 22lr bullet is 22 caliber, which is .22 inches. .22 * 2.54 would make it 0.5588 cm or 5.588 mm

2.54 cm per 1 inch... 10 mm in 1 cm

25.4 mm per 1 inch... 100 cal is 1 inch

0.254 mm is 1 caliber

45 ACP would be 11.43 mm
40 S&W would be 10.16 mm
9mm would be um 9 mm
22lr would be 5.59 mm
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Old 04-09-2012, 10:09 AM
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Nope. 1 Caliber is one Inch. 100 Caliber would be 100 Inches.
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Old 04-09-2012, 10:20 AM
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Originally Posted by Jungleboy View Post
Nope. 1 Caliber is one Inch. 100 Caliber would be 100 Inches.
Then by your reasoning a 50 caliber is 50 inches in diameter at the muzzle, a 38 caliber is 38 inches and a 357 magnum is 357 inches. You might want to back away from that one about 3 steps and take another look.


Can you imagine shooting a little 26 oz squirrel with a 22" projectile. Whooo-weee, won't have to skin that one.
Old 04-09-2012, 10:36 AM
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.50 cal = 12.7mm

diameter in inches, add decimal point in front of caliber , ex. 38 caliber becomes .38 in

Multiply the diameter in inches by 25.4---the number of millimeters in an inch---to convert the size to millimeters. For example, .30 inches x 25.4 mm/inch = 7.62 mm.

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Old 04-09-2012, 10:39 AM
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Quote:
Originally Posted by Old Grump View Post
Then by your reasoning a 50 caliber is 50 inches in diameter at the muzzle, a 38 caliber is 38 inches and a 357 magnum is 357 inches. You might want to back away from that one about 3 steps and take another look.


Can you imagine shooting a little 26 oz squirrel with a 22" projectile. Whooo-weee, won't have to skin that one.
NO! You and the OP have Forgotten the Decimal Point. 1.0 Caliber, is indeed one Inch. .50 Cal is half an Inch.
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Old 04-09-2012, 10:43 AM
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Unless you find one of the cartridges that has the caliber measured from the groove instead of the lands (see the Lazzeroni cartridges).
Old 04-09-2012, 10:50 AM
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concur with jungleboy...

also note that direct conversions are not very useful when comparing calibers... this is due to the arbitrary naming convention for certain ones...

for example (for jacketed rounds)
a 38 special is actually .357 in diameter
a 44 mag or special is actually .429
a 357 sig is actually .355 (same as 9mm)
a 380 is actually .355
a .223 is actually .224
a .45 is actually .451
a .303 british (or 7.7 arisaka) is actually .310
a 8mm mauser is actually 7.92 or .323

direct coversions are almost pointless in firearms
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Old 04-09-2012, 10:58 AM
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.38 cal originally was based on the outside diameter of the casing. As mefunkymxw said, most of the chamberings are arbitrary designations, related to the numeric designation but not necessarily exactly conforming to it.
Old 04-09-2012, 11:19 AM
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Is there a point to this thread, it is unlikely any of us will go to a local store and ask for 5.59 mm bullets for our 10/22's.
Old 04-09-2012, 11:21 AM
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LOL Im gonna go into Wal Mart and ask for their finest 10.16mm ammo and watch the guy look for 15 min! "C'mon I know its in there! I just bought some yesterday!"
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Old 04-09-2012, 12:35 PM
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Quote:
Originally Posted by Jungleboy View Post
NO! You and the OP have Forgotten the Decimal Point. 1.0 Caliber, is indeed one Inch. .50 Cal is half an Inch.
Nope, didn't forget, I had to go back and take the decimal points off my numbers to make the joke work. Being a stickler for accuracy I abhor the practice of calling a 38 special a 38 and not a .357 because of the case dimensions and a .429 a 44 magnum but a .41 cal a 41 magnum. They were doing it long before I came along, (believe it or not), and I don't think they will ever change unless we gradually shift everything to metric which would be a good thing, mostly,
Old 04-09-2012, 12:43 PM
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here in metric blighty you can order any size of ammo metric or imperial, . must admit though a .22 is normally said to be 5.5mm and a .177 is 4.5mm
Old 04-09-2012, 02:40 PM
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Okay, so my decimal place was off by 00.... I am a government worker. Probably time to get a job working at the IRS.

I will have to do that... I will have to call up Walmart and ask for some 11.43mm Auto
Old 04-09-2012, 06:34 PM
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Quote:
Originally Posted by NETWizz View Post
Well as most of you figured out, mm is metric for millimeter. In fact, it almost insults your intelligence to bring it up.

A 9mm bullet is 9mm, which is .9 cm

In contrast, caliber is hundredths of inches, so a 1 caliber bullet would be 1/100th of an inch.

A 50 caliber bullet would be 50/100ths or 1/2" in diameter.
************************************************

2.54 cm per inch is the conversion from metric to standard.

It can be said that a 22lr bullet is 22 caliber, which is .22 inches. .22 * 2.54 would make it 0.5588 cm or 5.588 mm

2.54 cm per 1 inch... 10 mm in 1 cm

25.4 mm per 1 inch... 100 cal is 1 inch

0.254 mm is 1 caliber

45 ACP would be 11.43 mm
40 S&W would be 10.16 mm
9mm would be um 9 mm
22lr would be 5.59 mm

Conversely divide the mm by 2.54 to find the caliber, for example:

.9 / 2.54 = .354 caliber
Old 04-09-2012, 06:37 PM
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Quote:
Originally Posted by NETWizz View Post
Okay, so my decimal place was off by 00.... I am a government worker. Probably time to get a job working at the IRS.

I will have to do that... I will have to call up Walmart and ask for some 11.43mm Auto

Must work in Congressional Budget Office....... explains a few things
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Old 04-09-2012, 07:35 PM
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If he was with the GSA, there would've been a song about it.......
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