HB-9 updated text (PDF) - Corbin Bullet Swaging

lows the hot lead out with a bang. You need to be reasonably careful
about fire and burns, and about potentially toxic fumes (no eating or smoking,
plenty of good ventilation). After about half an hour of this melting
and preparation, you are ready to start casting bullets.
The first few attempts usually make incomplete or frosty bullets, until
the mould is warmed up. During the casting process, the mould contains
liquid metal that is cooled to solidify on every single bullet made, so it is
constantly changing diameter from thermal expansion.
When you open the split halves, part of the mould is exposed to room
temperature air while the rest is protected from it, which cannot fail to
slightly warp the roundness of the mould. The two halves of the mould
cannot be put together with zero tolerance, as they would be far too hard
to swing open and closed again, so there is some degree of “slop” in the fit
of the pivot and the alignment pins. Add up all these factors and you can
see that a cast bullet has a limit of roundness and diameter control based
on physics, rather than skill or quality of manufacture.
In contrast, a swaging die runs at room temperature and does not
contact hot metal. It flows the metal under tons of pressure, squeezing
out all air pockets and voids. The bullet takes its shape and finish from the
diamond-lapped hardened surface of the die. The die is not split, but is a
solid tube or cylinder with thick walls to hold the pressure. The bullet
material goes in one end, and is pushed back out the same way. Two
precisely fitted punches seal both ends of the die. One moves in and out
to load material, and the other acts as an ejector.
The problems associated with heat expansion, swinging split section
alignment, and the time required to prepare are absent or minimized with
swaging. In addition, the die can make a wide range of weights depending
on how much material you put into it. A mould makes approximately
one weight because you must fill it to make a bullet. These are just a few
of the differences between casting and swaging.
There is one thing you can do more quickly and easily with casting
than with swaging: you can form a lead bullet with grooves for lubrication.
With swage dies, the bullet goes in and then comes back out the
same hole in the die. If you think about that for a minute, you will understand
that it would not be possible to swage a groove into the side of the
bullet and then push it back out of the die. The die would have to be
“split” like a mold. While this is possible, it is not cost effective. Fortunately,
you can roll grooves into a swaged lead bullet with a grooving tool
made by Corbin, or use better bullet designs or surface lubricants that
eliminate the need for grooves. And you can swage jacketed bullets, so
that separate lubricant is not required.
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