On Thu, 05 Sep 2013 11:41:19 -0700, pyotr filipivich
wrote:

Greetings

I have a couple questions on bullet sizes and barrel thickness.

In order to keep my hand in over summer break, I'm in the midst of
a CAD project. Maybe I can learn a few things too, about CAD, Catia
and the object of my project.
Yes, for "grins and giggles", I am attempting to gin up drawings
for the 6.35 mm "Pistola Con Caricato". The three barrel 18 shot one
off from the 1920's. Yeah, that one.
So, I have the SAAMI pdf with the dimension of the standard .25
cal / 6.35x16mmSR Browning cartridge. "Way cool" - but it did cause a
bit of "redrawing" as I had made preliminary drawings with a dimension
of 6.35 mm. "oops" (Actually, I was trying to get the geometry
sorted out, how to get lines to start where I wanted them, instead of
the apparent random location the program defaults to.)
Anyway, I now have a nice profile of a standard 6.36x16mmSR round
- bullet and cartridge. [23.11 mm OAL, as per spec]. What I don't
know however is: how long is the bullet itself?
"As Drawn" the bullet has nothing inside the brass to hold it
together. While this may not be a serious problem for merely drafting
a chamber for the cartridge, it offends my Professional Standards to
not have a "real bullet" correctly sized which can then be matched up
with the cartridge, and then that Assembly inserted into the Cylinder
Unit.

So, my questions:
1) Does anyone have the specs for the bullets themselves? Or a
link to where those same specs can be found?

Bullet diameter is 0.251".

2) Barrel dimensions. I have learned so far that the 25ACP is a
"low power" round, so barrel thickness is not a serious matter. I'm
guesstimating from the half dozen available photos somewhere around 2
to 3 mm thickness, which gives a diameter of 10.35 to 11.35 mm, if
based off the bullet diameter, 11 to 13 mm if base off the cartridge
diameter.

If you look up factory loaded pressures and perhaps double them for a
minimum you should be able to determine minimum barrel thickness.

[FWI, I have set this up with the semi-deranged idea that I can
change a few constants and viola - scale it up to .38, 38 Special,
357, 40 S&W or 45 ACP. Or down to a .22 short. Or whatever. [.600
Nitro Express? .50 BMG?]

So, I need a formula of some sort, or a reference chart, that will
provide me with some kind of ball park figure for the actual barrel
thickness ( radius of the out side of the barrel minus the bore
radius). As in "If you were going to bore a hole the length of a steel
round to serve as a barrel, what radius/diameter round would you
need?"

Calculate chamber pressure add a healthy "fudge factor" and you'll
have the minimum thickness. which, I believe you will find is far
thinner then you will want to make them.

(As I sit here, I realize I can start by boring a hole in a 6 inch
cube, then turn the cube down concentric to the axis, until I get a
barrel radius of the size I want. But that size is also determined by
the strength of the material, the pressure in the chamber, intended
amount felt recoil, and so forth. But I don't know what outside
diameter should be. (Yeah, I know - "About that much, plus or minus a
quart...")

Exactly.

So, does anyone have ballpark figures for determining barrel
dimensions, based upon the size bullet / cartridge it is to fire? Part
of me thinks even an "X is safe, plus a safety margin of Y%" would
work. At least for a "proof of concept" silliness.

Won't work that way. A barrel intended to shoot a .25" bullet of X
weight at 1,000 FPS will require a minimum strength different
thickness then a barrel intended for a .25" bullet of X weight at
3,000 FPS.

I think I am going to have to take that class on materials
properties.


tschus
pyotr

--
pyotr filipivich.
Discussing the decline in the US's tech edge, James Niccol once wrote
"It used to be that the USA was pretty good at producing stuff teenaged
boys could lose a finger or two playing with."
--
Cheers,

John B.