From: "E.J. Totty", [EMAIL PROTECTED]
[...]
No. 0.308" is the diameter or calibre of
the bullet. The rifle bore diameter/calibre is 0.300"
(0.2998" at the breech end for most Border 30 cal.
barrels, so I generally use a 0.2996" reamer pilot
bushing. The bore diameter at the muzzle is usually
0.0002" smaller. Each barrel maker may vary these
dimensions to suit his intended clientele.
[...]
Peter's item above jogged my memory
of the following, which I thought would interest the
list members.
I don't know who else might be aware of
this, but consider it another piece of information in
the gun owner's knowledge base:
A recent issue of the "Boeing News" had
an article about making machine gun barrels for the
various 20 & 30 mm Gatling and chain guns.
The essence of the article was about the
cost savings of a new process that is now used to
inexpensively manufacture and provide longer lived
barrels to the various customers.
The process: A steel barrel blank, has a
copper mandrel with the proper rifling pitch machined
into it, placed within; then plain old saltwater is flushed
through the space between the barrel and the
machined grooves in the mandrel while an electric current
is applied between the metals (lack of specifics here).
The resulting finished product is said to lack
all of the usual machining stresses, has a more predictable
and uniform result (unit to unit variations being
nonexistent), and the lifetime of the barrels are proven
to be significantly greater than those produced using
any of the current mechanical processes in existence.
The cost savings were that the saltwater was
processed to remove the etched metal (it too reclaimed),
and the saltwater was reused continually.
In the past, Steve, you have commented that
it wouldn't be long before a complete CNC program was
posted to the web, and not long thereafter that inexpensive
CNC machines would be an affordable thing to the average
gunner.
Now, all you need is a source of copper rods,
a regular lathe with a pitch (for making screws) attachment,
some bagged salt, everyday water, and a variable DC power
supply. And, with a barrel blank of your own, you can impart
whatever pitch you desire to the barrel!
That in itself saves a significant amount of time and
money in tools, and expertise.
The process spoken of is not unlike chem-milling,
which is used extensively to manufacture aircraft skins, and
the like.
ET
--
You're describing ECM rifling, which is used in Russian and
Bulgarian AKs and some makers of sporting rifles are starting to
use it. I think STI do their barrels with ECM. ECM stands
for Electro-Cathode Machining.
It's not quite that simple but it's certainly easier than
cut rifling.
Steve.
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