Jul/Aug - uspsa

in a semi-auto versus a bolt action is the
force needed to chamber a round. In a
bolt action you have your entire arm
working on the bolt handle to force the
cartridge into the chamber, plus the
camming action of the bolt lugs. This
can be a tremendous amount of force.
The semi-auto has only the spring
pushing the bolt. This spring is much
weaker than the force you can apply in
a bolt action, so anything that prevents
the cartridge from chambering easily
can cause a malfunction.
To eliminate potential problems
here, full-length resizing is a must. Bolt
guns may get away with neck sizing,
thanks to the force that can be applied
to chamber the round. However, if the
shoulder is not pushed back slightly
(say 0.005"), the effort to chamber the
round is increased, regardless of the
gun.
Some shooters have found they
need even more sizing than a standard
full-length sizing die will provide. A
"small base" die re-sizes the case further
down the body of the casing.
They do work the brass more, but that
is a small price for improved reliability.
When reloading for rifles, case
length and case neck thickness are
much more important than they are
with a pistol. The higher pressures
found in rifle cartridges tends to flow
the brass forward while pushing the
bullet through the bore. This can increase
the length of the casing in only
one or two firings, depending on the
cartridge. The normal trim length is
0.010" below maximum. If the case
grows too long, it causes problems by
hitting the end of the chamber and entering
the throat area. In a bolt gun this
round may still chamber (and fire at elevated
pressures), but in a semi, the
spring may not push the cartridge forward
sufficiently to allow the gun to go
in battery. We really don't want the
gun to go in battery with a long casing,
but we also don't want to clear malfunctions
caused by our oversize reloads.
As the case grows in length, the
neck thickness can also increase. This is
not as easily seen, nor is it as easy to
correct as with trimming. Eventually,
the case neck can become so thick that
the loaded round will not fit the chamber
neck, and cause a range of malfunctions
ranging from failures-tochamber,
to over-pressure caused by
impaired bullet release. Thick case
necks must either be reamed (removing
inside-diameter material) or turned
(removing outside-diameter material).
Turning is preferred, giving a more uniform
neck thickness. Reaming may
leave the neck thickness variable,
though that is still better than too
thick.
Many bolt action shooters, and
some high power shooters using semiautomatics,
will seat the bullet long to
be closer to the rifling, imitating the
benchrest shooters. This does not promote
best functioning in a semi. Assuming
the ammunition will still fit in
the magazine, in some cases the bullet
may contact the rifling, and, as with
case length and neck thickness, cause
problems with functioning or pressure.
Conventional wisdom says the bullet
must be crimped for use in semi-autos.
In a word — maybe. The point of
a crimp is to ensure the bullet does not
move under the conditions and handling
it is subjected to. Military and
commercial ammunition is commonly
crimped simply because the military
wants ammunition that will survive
anything — and they may subject it to
many adversities never seen by commercial
ammunition. Commercial ammunition
is built to be rugged because
the factory does not know what the
user will subject the ammunition to.
For your own use, applying a crimp
may not be needed. We will not be subjecting
the ammunition to extreme
conditions, but we must ensure the bullet
stays put. Generally, the severest
handling this ammo will experience is
the trip from the magazine to the
chamber. This happens very quickly
and will normally be the greatest force
applied to the cartridge other than firing.
I advise people to test to see if they
need a crimp. Load, say, five rounds,
including one with no crimp. Measure
the uncrimped one for length and be
certain you can differentiate between
tip damage and bullet movement. Fire
each of the other four, having the test
round feed into the chamber each time.
This requires some juggling of taking
the round out after each shot and repositioning
it in the magazine, but it is a
test, so it does not have to be done often.
Once the other four rounds have
been fired, re-measure the cartridge to
determine if the bullet has moved. If it
has, you may need to crimp. You may
also be able to use a slightly smaller expander
ball to allow the case to grip the
bullet tighter. If you can detect no
movement of the bullet, there is little
need to crimp. You may want to experiment
with a crimp anyway to see
how it affects accuracy — sometimes it
helps.
I've talked about the utility of a cartridge
gauge in the past with respect to
handgun ammunition. It applies
equally well to rifle. Dillon in particular
makes cartridge gauges for the most
popular rifle cartridges. These gauges
are normally a bit tighter than a standard
chamber, so if the cartridge drops
into the gauge fully, there should be no
problem when chambering. The gaup
will also show if there is a length problem
as well as show if the cartridge conforms
to normal headspace. Overall,
these gauges are good tools for helping
ensure reliable performance.
Semi-autos are much harder on
cases than bolt guns for obvious reasons.
However, some guns are much
worse than others. Most people will
not try to reload cases coming out of an
H&K, for instance. These guns almost
shoot two projectiles, the bullet and
the casing. Even in mild-mannered
guns, the rim may be bent, or there
may be deep dings in the case mouth or
body that could lead to a case failure.
Case inspection is important.
Military guns also have unrestrained
firing pins. This means the firing
pin is free to move around during
cycling of the action. If you extract an
unfired round, one having been fed
into the chamber from firing a previous
round, it will almost always have a
slight dimple in the primer from the
firing pin. This means we do not want
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July/August 2002 • FRONT SIGHT 49