Updated 7x61 Super Data

Load Development
Updated 7x61 Super Data
By Mike Thomas
T
here is a fair amount of
published load data available for the 7x61, though
it’s virtually all quite dated. Norma
increased the powder capacity of the
original case during the 1960s and
subsequently renamed it the 7x61
Super, but most shooters continue
to refer to this magnum as the 7x61
Sharpe & Hart.
For this handloading endeavor,
a NULA Model 28 7x61 with a
26-inch No. 3 contour Douglas
stainless barrel (one-in-10-inch
twist) was used. The rifle weighs
6.2 pounds. A Leupold VX-3 2.58x 36mm scope in Talley lightweight rings added exactly one more
pound.
From a handloader’s perspective,
there are some important cautionary points regarding the 7x61 that
are not generally applicable to
“commercial” rounds. It appears
that most, perhaps all, Schultz &
Larsen rifles had factory freebored
throats. With regard to custom rifles
in 7x61, some may have freebore,
while others, like the NULA, do
not. There is a review of a Schultz &
Larsen Model 60 in the December
1957 American Rifleman that mentions a 1⁄4-inch freebore. So does an
old Lyman manual (No. 44) from
1967 in a description of its Schultz
& Larsen Model 65DL test rifle. Lyman recommended reducing loads
5 percent for non-freebored guns.
Ken Waters also covered the matter
in his 1974 7x61 “Pet Loads” article
(Handloader No. 47). Regardless
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LOAD DEVELOPMENT • April 2015
Bullets used in developing updated 7x61 data (left to right): Barnes 140-grain TTSX BT and 150 TSX BT,
Sierra 150 GameKing SBT, Hornady 154 InterLock SP, Nosler 160 Partition, Sierra 160 GameKing SBT,
Speer 160 DeepCurl and Hornady 175-grain InterLock SP.
of a 7x61 rifle’s origin, throat type
should be determined before working up handloads.
Depending on the source, specifications for case dimensions, namely
Not all groups from the NULA 7x61 test rifle were
under .5 inch, but enough were to realize the rifle/
cartridge combination has accuracy potential for
any game hunting situation.
overall length and neck diameter,
also vary. A chamber cast should
be in order for anyone with doubts
about the dimensions of a chamber,
particularly if the rifle is anything
other than an original Schultz &
Larsen. Published figures on maximum allowable neck diameters differ considerably. The Norma factory
ammunition I have (circa 1970s) has
an outside diameter averaging .3138
inch. After firing in the NULA, the
neck diameter measures .319 inch.
Maximum overall cartridge length
may be listed anywhere between
2.394 to 2.402 inches, the latter
most common. This is the figure
Ken Waters used in his 1974 article.
Published shoulder angles also vary
from 37 to 44 degrees, but most
sources list it at 44. Ken Waters
called it 43 degrees, 12 minutes.
Another caveat is the redesign of
the 7x61 Sharpe & Hart case. Outside dimensions, of course, remained
Six powders were used in developing the loads
listed in the table. Federal 215 Magnum Match
primers were used for all loads.
the same. Internally, the web and
case walls were thinned somewhat
to increase powder capacity. The
newer case became the Norma 7x61
Super. Such cases (recent production from Norma) were used for the
data in this article. Water capacity
is 76 grains. Original 7x61 brass has
a water capacity of approximately
71 grains. By comparison, the 7mm
Remington Magnum case averages
around 81.6 grains. Early 7x61 brass
is probably still out there and being
loaded, old as it may be. The matter
is further compounded by a myriad
of 7x61 brass that has been reformed from other magnum cases.
As a result, there are significant
variances in powder capacities. In
light of all this, handloaders should
treat the 7x61 with the extra caution
reserved for wildcat cartridges.
I discovered a couple of characteristic features of NULA rifles when
I worked with my first one several
years ago. First, forget spent primer
appearance as an indication of high
loaddata.com
pressure. This once favored method
of judging pressure has been proven
to be less than reliable on several
counts. The same can be said for
measuring case head expansion and
pressure ring expansion. In a NULA
.308 Winchester that has had well
more than 1,000 handloaded rounds
fired in it, I have yet to observe anything resembling a flattened primer.
The 7x61 responds like the .308 in
this regard – spent primers all look
the same despite varying charges of
different powders.
Secondly, what about heavy bolt
lift as an indication of high pressure?
This is usually a sign of excessive
pressure, in fact, probably pressure well beyond excessive. Melvin
Forbes reiterated by stating that
heavy bolt lift will normally be the
first high-pressure symptom in one
of his rifles. However, it’s important
to note that everything fits closely
in a NULA action. Bolt closing and
bolt lift require a little more exertion, whether there is a cartridge
in the chamber or not, than most
mass-produced, bolt-action rifles,
but one quickly develops a feeling
for the slight extra effort required.
These cautionary points are
emphasized, as it was necessary
to develop new 7x61 loads using
components that were not available almost 40 years ago when Ken
Waters did the Handloader article. A
variety of checks were used to ensure
that all data was safe in the test rifle.
With normal judicious handloading
procedures that included taking into
account the previously mentioned
factors regarding the 7x61, loads in
the data table appeared to be safe in
the test rifle.
From left: Norma 7x61 Super (formerly 7x61
Sharpe & Hart Magnum) and the 7mm Remington
Magnum. Actual performance difference between
the two is small, but the 7x61 lost out in popularity because of superior marketing by Remington,
availability and the fact that it was chambered in
an affordable rifle.
April 2015 • LOAD DEVELOPMENT
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Load Development
Norma produces 7x61 Super unprimed brass that
is sold by several dealers in the U.S.
A “Load from a Disk” computer
program was one method employed
in developing load data. It uses variables, such as case capacity, bullet
length and seating depth, in computing data with approximate velocity and chamber pressure. Primers
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LOAD DEVELOPMENT • April 2015
are not included in computations
and neither are all the suitable newer
powders. While the program might
be a bit lacking, it can be used as an
approximate guide. Actual results
(muzzle velocities) can be close
enough to the program’s predictions
to make its use worthwhile. Remember, however, that this is not a loading manual.
With some of the older powders,
like Hodgdon H-4831, data is available in at least two modern loading
manuals, the Sierra 5th Edition and
the Hornady 8th Edition. Though
the books may be fairly recent, a
cursory glance indicates the data is
probably old. Nevertheless, many
of the listed powders are currently
produced. Considering burning
rates may have changed slightly over
the years, starting loads should be
reduced accordingly. Many manuals from the 1950s and 1960s have
data using IMR-4350 and H-4831,
as well as other powders; charge
weights are often all over the place,
and some of the loads would be
dangerous with the powder available
today.
John Barsness researched and
quantified a process for load data
workup in the mid-1990s (Rifle No.
163). Basically, his formula involves
velocity increasing at one-fourth the
rate of case capacity. As an example,
a Nosler 7mm 150-grain Partition
bullet (1.203 inches) is seated to
an overall length of 3.27 inches in
a 7mm Remington Magnum case.
This leaves a water capacity of 74.6
grains. The same bullet seated to an
overall length of 3.21 inches for the
7x61 Super leaves a capacity of 69.8
grains. The difference, 4.8 grains,
equals a 6.9 percent case capacity advantage for the Remington
cartridge. Dividing by 4 (to obtain
the velocity difference) equals 1.7
percent greater velocity for the 7mm
Remington Magnum with barrels
of the same length. However, most
sporting and pressure barrels for the
Remington cartridge are 24 inches.
Average maximum muzzle velocity
(from load manuals) for 150-grain
bullets is 3,014 fps. The 7x61’s
maximum velocity should be approximately 3,014, less 1.7 percent.
That equals 51 fps. The NULA
has a 26-inch barrel, however, so
velocity in this instance should be
about the same as 7mm Remington
Magnum bullets fired in a 24-inch
barrel. Figures for other bullets are
slightly different, of course, but the
4-to-1 ratio remains. The chronograph can be a major factor in developing loads where no data exists.
Loading manuals’ 7mm Remington Magnum average maximum muzzle velocities are as
follows: 140-grain bullets = 3,117
fps; 150-grain bullets = 3,014 fps;
160-grain bullets = 2,915 fps; 175grain bullets = 2,777 fps.
Preferring to err on the side of
safety, and the fact that the 7x61
data is not pressure-tested, I kept
most maximum muzzle velocities
slightly below those of the 7mm
Remington Magnum maximum average figures. The reduction should
be considered as insignificant in
terms of performance. Brass life has
been excellent, and primer pockets
remain tight.
The data table is self-explanatory,
but a few points bear mentioning
here. Federal 215 Magnum Match
primers were used exclusively.
Regarding the Speer 160-grain
DeepCurl bullet, I have used only
one DeepCurl design previously, a
150-grainer in a .270 Winchester.
They were exceptionally accurate with little load development
required. An oversized outside
diameter of .280 inch rather than
.277 inch may have been a major
contributory factor to the accuracy.
With the 7mm DeepCurl, a sample
of three bullets averaged .2847 inch,
quite a bit larger than other 7mm
loaddata.com
bullets. Depending on chamber
dimensions, their use in a 7x61 rifle
may likely necessitate turning case
loaddata.com
necks for adequate clearance. All
shooting was done during several
range sessions. Average temperature
was around 40 degrees Fahrenheit.
The loads have yet to be fired in
100-degree Texas heat.
April 2015 • LOAD DEVELOPMENT
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