Shooting Sports USA - August 2014 - 31

Gas
The foundation for "no commercial ammo
in the Garand" advice lies with the Garand's
design, coupled with the difference between
Army specifications for ammunition pressures
and the Sporting Arms and Ammunition Manufacturer's Institute, Inc. (SAAMI) specifications
for modern .30-'06 ammunition pressures.
The Army's maximum allowable pressure for
its .30-'06 ammunition (M2 Ball) is 50,000 psi,
with a maximum proof test load pressure set at
67,500 psi1. In testing, Townsend Whelen found
that M2 Ball breech pressures were actually only
"about 42,000 pounds. 2 The SAAMI standard for
"
.30-'06, however, is 60,000 psi maximum average pressure, and the SAAMI standard for rifle
cartridge proof loads is 33 to 44 percent above
the maximum average pressure (MAP) for any
particular cartridge (in the .30-'06, that proof load
pressure is as high as 86,400 psi).3 As you can
see, at 60,000 psi the SAAMI allowable pressure
is almost half again as much as M2 Ball's actual
pressure and is 20 percent higher than the maximum allowed in the Garand. So, it's not too much
of an exaggeration to think of shooting commercial .30-'06 hunting ammunition in the Garand
as possibly feeding the rifle a diet of proof loads.
Again, the caution against using commercial
.30-'06 in the Garand lies in the pressures SAAMI
allows for commercial .30-'06. The brand or lot
number that you buy off the shelf may or may
not exceed the Garand's design limits. About the
only way for the layman to find out, is to shoot it
in his Garand and see if it eventually buggers up
the rifle.
When we talk about safe gas pressures in the
Garand, we're concerned not with just peak pressure, but also the pressure curve. That is, we're
concerned about the combination of force (gas
pressure) and the rate at which it is applied to the
gas system. John C. Garand designed his rifle to
operate properly with a pressure curve that won't
bash the gas system components around too
hard. More specifically, Mr. Garand designed his
rifle to shoot the M2 Ball already in manufacture
for the then-current issue M1903 rifles.

As the M2's original 42,000 psi pushes the
bullet down the bore, the increasing volume
between the chamber and the bullet drops the
pressure to about 8,000 psi2 near the muzzle,
where the port taps off about 6,000 psi
(+/- 2,000 psi)5 worth of that to operate the
Garand's gas system. As we know, the gas
pushes on the op rod, essentially a long piston
connected to the bolt, driving the bolt backward
to extract and eject the empty case and compressing the recoil spring inside the op rod. The recoil
spring then pushes the op rod forward again,
pulling the bolt with it to strip off and chamber a
fresh cartridge. All of this is in balance - the gas
pressure, the port size, the op rod's mass and the
recoil spring strength. Vary any one of these too
much, and the system fails to operate properly.
Now that we've established what we don't
want, let's talk about what's appropriate for
shooting in the Garand. Let's handload.

Powders
The cartridge, of course, started life as the
".30 Government" or the ".30-03," indicating it
being a .30 caliber cartridge intended for the
then-new 1903 Springfield rifle. Today, that heavy
220 gr. bullet seems slow at 2,300 fps, but it was
pretty high performance for its day. By shortening the neck a bit and lightening the bullet to
150 gr., velocity went up to 2,700 fps, and the
Army adopted the improved .30 Government in
1906, giving us the .30-'06. When ballisticians
found that a heavier bullet with a boat tail
extended the effective range of .30 caliber
machine guns, the bullet weight went up to
172 gr. at a slight cost in velocity, which dropped
to 2,640 fps. With the advent of the semiautomatic Garand and its gas system, however, the
government reduced bullet weight back to
150 gr. and designated the cartridge M2 Ball.
Military M2 Ball ammunition launches a
150 gr. FMJ bullet at 2,740 fps, using 50 grains of
IMR 4895.1 Military M72 Match ammunition
featured a 173 gr. bullet launched at 2640 fps.
The powder was, again, IMR 4895 and, again,
SHOOTINGSPORTSUSA.COM 31


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Shooting Sports USA - August 2014

Table of Contents for the Digital Edition of Shooting Sports USA - August 2014

Contents
Shooting Sports USA - August 2014 - Cover1
Shooting Sports USA - August 2014 - Cover2
Shooting Sports USA - August 2014 - 3
Shooting Sports USA - August 2014 - 4
Shooting Sports USA - August 2014 - 5
Shooting Sports USA - August 2014 - Contents
Shooting Sports USA - August 2014 - 7
Shooting Sports USA - August 2014 - 8
Shooting Sports USA - August 2014 - 9
Shooting Sports USA - August 2014 - 10
Shooting Sports USA - August 2014 - 11
Shooting Sports USA - August 2014 - 12
Shooting Sports USA - August 2014 - 13
Shooting Sports USA - August 2014 - 14
Shooting Sports USA - August 2014 - 15
Shooting Sports USA - August 2014 - 16
Shooting Sports USA - August 2014 - 17
Shooting Sports USA - August 2014 - 18
Shooting Sports USA - August 2014 - 19
Shooting Sports USA - August 2014 - 20
Shooting Sports USA - August 2014 - 21
Shooting Sports USA - August 2014 - 22
Shooting Sports USA - August 2014 - 23
Shooting Sports USA - August 2014 - 24
Shooting Sports USA - August 2014 - 25
Shooting Sports USA - August 2014 - 26
Shooting Sports USA - August 2014 - 27
Shooting Sports USA - August 2014 - 28
Shooting Sports USA - August 2014 - 29
Shooting Sports USA - August 2014 - 30
Shooting Sports USA - August 2014 - 31
Shooting Sports USA - August 2014 - 32
Shooting Sports USA - August 2014 - 33
Shooting Sports USA - August 2014 - 34
Shooting Sports USA - August 2014 - 35
Shooting Sports USA - August 2014 - 36
Shooting Sports USA - August 2014 - 37
Shooting Sports USA - August 2014 - 38
Shooting Sports USA - August 2014 - Cover3
Shooting Sports USA - August 2014 - Cover4
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