Gas checked bullets
Now, on the plus side, pure lead maintains the molecular
cohesion - that is, the resistance to breaking up - that has
always made it ideal for casting into bullets, and it also
expands reliably across a wide spectrum of velocities
resulting in an expanded mushroom inside the body cavity
of a game animal. And it is inexpensive.
The converse is that no matter what bullet material or
configuration you select, all bullets have limitations, and
soft lead is no exception. Muzzle velocities above 2,150fps
are close to the velocity limit above which the lead itself
can deform in flight due to nose pressure, and of course the
softer the lead the more bore-leading one can expect. Cast
bullets can exhibit serious flaws, such as uneven cores and
void, empty spaces, which can be overcome by swaging the
bullets - but most folks that I know here in Africa continue
to cast their bullets the old-fashioned way.
So, though the tendency has been to use jacketed bullets
in high-powered rifles, a bullet cast or swaged from slightly
harder lead and with a gas check - that cartridge equivalent
of a sabot - affixed is certainly a viable alternative. And it
can be a lot more fun, too.
There are a number of different methods of determining
the relative hardness of a metal, but the one used to rate the
hardness of lead in reloading circles is the Brinell (BHN)
scale, introduced by the Swedish engineer Johan Brinell in
1900. It works by measuring the indentation on a sample
caused by a known force applied through an indenter. Though
it is less well-suited to harder metals, it works ideally with
lead, where a BHN of 5.0 denotes pure lead, and various lead
alloys can go up to 35.0.
Hardness testers are not overly complicated, and are
available to any reloader or bullet caster - perhaps one of the
most common is the one that we use at my shooting club, the
LBT Hardness Tester. It is solidly constructed, and measures
BHN from 6.0-40.0. It takes you about ten seconds to test a
cast bullet, and the results are guaranteed accurate to 1 BHN.
Lee also offers a test kit that is designed to be used with a
reloading press, and there are others.
But even harder lead alloys, while still easy to work with
in terms of bullet casting, will still leave lead deposits in
the bore at higher velocities. I have a seemingly mirror-like
finish in the bore of my Colt .45 pistol, but firing cast bullets
at even moderate velocities of between 830-850fps will leave
annoying lead deposits in the bore. Which is why I shoot
Frontier FMJs in competition. But I digress. The solution is
the gas check, for which, of course, you need a gas-checked
bullet mould.
A gas check is a thin cup, usually crafted from copper,
zinc or aluminium alloy which is affixed to the base of a
lead cast bullet during the reloading process. Generally, gas
checks are used with higher-pressure and velocity cartridges
to prevent the buildup of lead in the barrel which enhances
accuracy. In order for a bullet to be fitted with a gas check it
requires a slightly rebated area at the base to allow the gas
check to be pressed in place whilst the bullet retains the same
diameter, and so the modification has to be incorporated into
the mould.
The gas check is effectively swaged onto the bullet,
covering most or all of the base, during the lubrisizing
process. Once fitted, the gas-checked bullet is loaded
conventionally.
When a high-powered, or magnum round is fired, the
high pressures allow propellant gas to escape past the bullet,
causing gas cutting of the base which increases lead deposits
http://www.africanhunteronline.com
Page 12 Hunter Vol. 19 No. 1
African