From: jesw@mitre.org (James Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Rifling, how is it done?
Date: 5 Sep 1997 18:47:14 GMT

In article <robd-ya02408000R0309971321390001@news.jump.net>,
robd@topdrawer.com (Rob) wrote:

> Also, I always wanted to know how such odd sizes of bores were
> chosen.  They don't seem to correspond to wire gauge of letter sizes, and
> most of them are not fractional sizes, so why were the dimesions chosen?

Most of the calibers date from 1850 - 1890 and are secretly metric. There
are 2 measurements, the bore size before rifling and the diameter across
the rifling groove bottoms, which is also the bullet diameter. The grooves
are typically around 0.004" deep.

.22 (0.223" or 0.224") was, I think, a French shotgun pellet size used by
Flobert (?) around 1840 in a percussion-cap-powered indoor target rifle.
It later grew a rim for extraction and a small powder charge and became
the .22 (Short, after others were introduced.)  .22 BB caps or
Flobert-Patronen are over 150 years old and still being made. Only paper
shotgun shells are older.

.243 is 6mm + 2x rifling groove depth.

.257 is ~6.5mm, or 1/4" plus grooves.

.264 is 6.5mm + rifling grooves. It was a Mauser and Mannlicher caliber
from the 1890's.

.270 (0.277") is ~7mm. "7mm" is actually 7mm + rifling grooves = 0.284".
"280" uses a "7mm" bullet.

.30/.303 or 7.5/7.6x/7.7mm came from the 1880's research of Swiss Col.
Edouard Rubin to find the ideal military caliber for the new smokeless
powder. The Belgian 1889 and Argentine 1891 Mausers used 7.65mm. The US
picked a .300" bore, .308" groove & bullet for the Krag rifle. We also
tried 6mm (236) way back then but the powder wasn't up to it.

The Russian caliber began as 3 "lines", which I think was originally a
French measurement unit. Their 1891 rifle is the one that accepts NATO 308
ammo but not vice versa (don't shoot it!), an amazing example of
cleverness and foresight.

The British 276 and 325 are really 7mm and 8mm.

.38" is the case diameter, .357" the bullet OD. Originally the cartridge
was made like a big .22, rimfire and with the bullet stepping up to the
same size as the case OD beyond the case mouth. Design evolution lead to
making bullets the case ID, giving a longer & more stable bore riding
surface. I'm not sure of the exact history, but .36 was the "Navy" caliber
for muzzle-loading pistols. The "Army" was .44, better against cavalry.

40 is ~10mm.

44 is really .429", another old one that started like a big .22.

The 45 Auto was developed for an Army spec that required at least .450"
bullets.

458 is a .45" bore with .004" grooves. .40" to .45" was found to be the
best for elongated self-sealing bullets such as Minie balls. Round balls
were .58", .69", or even more. They were chosen as so many balls per pound
instead of hole dimensions.

The British 465, 470, etc. came about due to laws prohibiting ammo in the
military 45 caliber in rebellious colonies.

Later cartridges may take numbers on either side of earlier ones. Thus
there are .224" diameter cartridges called 218, 219, 220, 221, 222, 223,
and 225.

James Wilkins
jesw@mitre.org

From: jesw@mitre.org (James Wilkins)
Subject: Re: Rifling, how is it done?
Date: Sep 08 1997
Newsgroups: rec.crafts.metalworking

In article <jesw-0509971447160001@m21664-mac.mitre.org>, jesw@mitre.org
(James Wilkins) wrote:

> The British 276 and 325 are really 7mm and 8mm. 
                      ^^^
Oops, I meant 318.

Cartridges of the World describes almost all of them, briefly. John
Taylor's African Rifles and Cartridges goes into much more detail and he
illustrates his points with brief but intense tales of his and other's
adventures hunting   dangerous game in thick cover, where the animal has a
very good chance of winning. The rifle partly makes up for our lack of
teeth and claws but the animal still has better eyes, ears, nose, strength
and speed.

James Wilkins
jesw@mitre.org