From: bercov@bevsun.bev.lbl.gov (John Bercovitz)
Subject: Re: 9mm Camp Carbine Ballistics
Organization: Lawrence Berkeley Laboratory, California

In article <47513@mimsy.umd.edu> lilianstrom@LEVY.FNAL.GOV (Be excellent to one another.....) writes:
#In article <47453@mimsy.umd.edu>, jpcallis@uokmax.ecn.uoknor.edu (James P. Callison) writes:

##It should hold 10 .38s as well. It's been awhile since I shot my dad's
##..357, but I think .357 and .38 are the same size--the .357 just has a
##stouter case and a bigger charge.

#         Actually the .357 case is .10 inches (I think) longer to
#         prevent the hotter .357 loads chambering in regular .38
#         special revolvers.  (Also allows more powder/power :=).)  The
#         same thought was used on .44 special to .44 magnum and  the
#         various .40 cal rounds.

Some gun writer started that a long time ago.  I used to know which one
it was, can't remember now.  The gun writers mostly copy each other so
it's the falsehood that refused to die, I guess.  I mean this one's been
around like _forever_.  The correct nominal figure is .135".  If you
measure actual cases, you'll find that this figure is pretty close.
(Nominal max. case length is 1.290 for 357 and 1.155 for 38 Spl.)

It's not that uncommon in mechanical engineering to give figures to the
nearest 1/10 inch, so maybe that's how it started.  For the general
population, fractions are more common so 1/8 inch would be a better
guess.  When a gun writer converts these fractions to .10 and .125
[so as to be _very_ precise ;-)] you get the decimal figures previously
mentioned in this thread.

       John Bercovitz     (JHBercovitz@lbl.gov)