24 | SPORTING SHOOTER _ MAY 2018
that the velocity reduction is
similar to the gain you get by
improving. Thus, if you get
an extra 100 fps from the
improved case you can expect
to lose about 100fps when
shooting standard ammo in
the improved chamber. This
may be a likely average, but I
found that the amount of loss
depends to some extent on the
burning rate of the powder
used in the factory ammo. For
instance in my first 6mm
Improved rifle the 80gn
Winchester factory load at an
advertised velocity of
3470fps actually chrono-d
3220fps, but the Remington
100gn Core-Lokt PSP load
advertised with a MV of
3100fps clocked 3073 fps - a
loss of less than 30 fps. So go
figure! In my experience, the
velocity gain in a majority of
improved cartridges is about
100fps. Ackley always
claimed the .257 Ackley
showed the largest gain,
and Hornady pegged the
increase at 100fps, while
some have gone overboard
claiming an increase of up to
300fps. My experiments with
the .243, the 6mm and .257
Ackley improved rounds
show an increase of 150fps is
possible without running
excessive pressures.
Regarding the theory that
improving a case reduces bolt
thrust, the amount of
reduction is insignificant.
The claim is based on the
premise that the forward
portion of the straight-walled
case exerts more of a grip on
the chamber wall than a
tapered case to keep the case
anchored firmly in the
chamber. This grip,
supposedly prevents the case
from moving rearward
against the bolt face, therefore
reducing the force exerted
against the bolt. Waal maybe!
But that's not the whole
story. The last 9.5mm or so of
the case head never grips the
chamber anyway, unless
excessive pressure swells the
solid head of the case. No
matter whether the cartridge
is standard or improved, it
firmly grips the chamber wall
with its forward portion,
while internal pressure acts
to push the case head
rearward, so the possible
reduction in backthrust is
only 750 to 1000lbs for an
average-size cartridge case.
What exactly is the potential
bolt thrust? For a .300
Magnum, the total potential
rearward force against the
inside of the case head is
about 7,500 lbs. This means
that the maximum reduction
you can expect in this
example is only about 13
percent. In most cartridges
however, the cartridge
sidewall never ever gets
stretched to the 750 lb level,
which is a blessing. That
leaves the effective real
reduction on back thrust
against the bolt very small, or
even zero. I know that this
reduction in backthrust has
been credited with making
improved cartridges which
have been loaded to
maximum working pressure
easier to extract, but the
reality is: it is just too little to
offer any real advantage.The Obsolete
.275 H&H MagnumQ
Can you tell me which
cartridge was the first
7mm Magnum? I’ve been told
that it was the 7x73mm VomHofe belted which dates back to- But I’m dubious about this
and so am writing to ask you.
- Fred Anderson
A
The first 7mm belted
magnum was the British
.275 H&H Magnum which
appeared in 1912. The first
hunter to test the then new
cartridge was Frederick
Courtenay Selous who used it
on plains game in East Africa
in 1914. The .275 is the
granddaddy of the 7mm
Magnums and factory
ballistics obtained with a
double-based flake powder of
a 160gn bullet at 2675fps and a
175 grainer at 2690fps were
nothing to celebrate in song
and story today. It was loaded
in the U.S by Western
cartridge Company until about
1939, and it inspired the
development of wildcat and
improved versions, the first of
which was the .276 Dubiel
Magnum. In rapid succession,
in the post-war years, along
came the 7mm Ackley
Magnum, the 7mm Weatherby
Magnum, the 7x61 Sharpe &
Hart and finally the 7mm
Remington Magnum. Thereby
hangs a tale: Jack O’Connor
hunted elk with Les Bowman
in Wyoming and on leaving
gifted him the rifle he used - a
.275 H&H Magnum. Les had
the gun rechambered for the
.338 Win. Mag. case neckeddown to shoot 7mm bullets
and called it the .280 Rem.
Mag. Later, when Wayne Leek,
chief designer for Remington
came to hunt with Les, he
used the 7mm-338 and was so
impressed that he set out to
convince the company to bring
it out as the 7mm Rem. Mag.
The rest, as they say, is history.Calibre No Mystery
Q
I’ve been given an old
German single-shot rifle
made by Geco and I’d like to
shoot it if ammo is available.
The barrel is marked:
“5.6x35R” which no gunshop
I’ve asked seems to have any
knowledge of. Can you tell me
what it is? Are any ammo or
cases available for it? Where
can I find loading data? I have
a Super Simplex press and a
Master Turret Press, if that’s
any help.- Bill Sparrow
A
When the black powder
.22 WCF was adopted for
use in Germany in the 1890s
it was was loaded with
smokeless powder to a higher
velocity long before
wildcatters created the .22
Hornet in the U.S.A. Dynamit
Nobel’s reloading digest lists
two loads with powder
charges of 6.6 and 9.3 grains
giving muzzle velocities of
1700 and 2200fps. It became a
popular small game and target
round in Europe. Its metric
designation was 5.6x35R
Vierling, to separate it from
the regular 5.6x35R (the .22
Hornet). The proper bullet
diameter for the Vierling is
.222”; for the Hornet it used
to be .223, but today is more
likely to be .224”. This makes
it unsafe to shoot .22 Hornet
in the Vierling chamber.
However, you can shoot
your rifle using Hornet cases
reloaded with .222” bullets,
and Hornet loading data.
If you have .222 dies for
your Super Simplex, get a
Hornet shellholder and you
are all set.The extra case
volume really
does give the
Ackley version
a discernable
edge.”
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