Updated 7x61 Super Data

Load Development

Updated 7x61 Super Data

By Mike Thomas

There 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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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

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



Six powders were used in developing the loads listed in the table. Federal 215 Magnum Match primers were used for all loads.

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 2

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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3 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



bullets. Depending on chamber dimensions, their use in a 7x61 rifle may likely necessitate turning case



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.

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