7.62 Jonson

.300 WinMag; .308 Win; 7.62 Jonson; .416 Rigby;

Type  Rifle
Place of origin  USA
Production history
Designer  Jonson Arms Laboratories
Designed  1983
Manufacturer  Jonson Arms Laboratories
Produced  1985-Present
Specifications
Bullet diameter  .308 in (7.8 mm)
Neck diameter  .343 in (8.7 mm)
Shoulder diameter  .574 in (14.6 mm)
Base diameter  .590 in (15.0 mm)
Rim diameter  .590 in (15.0 mm)
Case length  2.030 in (51.6 mm)
Overall length  2.810 in (71.4 mm)
Rifling twist  1-10"
Primer type  Large rifle magnum
Ballistic performance
Bullet weight/type  Velocity  Energy
150 gr (9.7 g) SP  3,357 ft/s (1,023 m/s)  3,753 ft·lbf (5,088 J)
165 gr (10.7 g) HP  3,277 ft/s (999 m/s)  3,935 ft·lbf (5,335 J)
180 gr (12 g) HP  3,136 ft/s (956 m/s)  3,931 ft·lbf (5,330 J)
200 gr (13 g) SP  2,935 ft/s (895 m/s)  3,826 ft·lbf (5,187 J)
Test barrel length: 24"
Source: [1]



7.62 Jonson (also known as The Big Jonson and .30 PPC), is a .308 caliber short action, centerfire rifle cartridge that was introduced in 1985 by Jonson Arms Laboratories. The cartridge overall length is 71.37mm, cartridge case is 51.56mm in length and the bullet diameter is 7.62 mm (common to all U.S. .30 caliber cartridges). The design and introduction of the 7.62 Jonson cartridge preceded all so-called short magnum rounds, except for the .350 Remington Magnum, by at least 10 years. Jonson rounds may be the first commercial rifle cartridges in history to be designed by computer algorithm.

Contents
    * 1 History & Development
    * 2 Adoption versus Adaptation
    * 3 Design Advantage
    * 4 Use & Performance
    * 5 Comparison
    * 6 References

History & Development

The design for Jonson rounds was inspired by the three most important cartridge lineages of modern times. First, exhaustive research went into characteristics of the 6mm PPC and .22 PPC benchrest rounds designed by Palmisano & Pindel in the early 1970s[1][2]. Design characteristics were also incorporated from the .300 Savage, which served as the parent to the .308 Winchester (7.62x51mm NATO) cartridge, a round that was developed for the US armed forces in the 1950s and which is still in use today.[3] From the first ever short magnum round, the .350 Remington Magnum, the culmination of the great H&H, belted magnum lineage, came the antithetical idea of removing the belt. Since a dimensioned .30 PPC design proved not viable, Jonson Labs authored a computer algorithm to optimize the round and in 1984, copyrighted the algorithm that produced The Jonson Factor and also the resulting case design. When the factor was applied to the Jonson .30 PPC-like design, the round proved to incorporate a perfected ballistic profile, designated parallactic precision. The main advantages to the design were improved accuracy through a more consistent powder burn and lower than expected realized recoil per caliber. An entire family of Jonson rounds has since been spawned based on the Jonson Factor.

Adoption versus Adaptation

In the early 1990s, extensive discussion involving the Jonson design occurred on gun forums like rec.guns and many of the design parameters were shared freely with other gun aficionados, where the idea, if not all cartridge parameters, became part of the public domain. Since then, several companies have built cartridges using the design, which action clearly honors Jonson Labs' earlier work. At least one proprietary round uses the exact nomenclature designated in 1985 by Jonson Labs as the provisional name for their early test rounds. Adoption is an accepted practice in the gun world and one which manufacturers have used for decades to take advantage of the marketplace.[4]

Design Advantage

For practical reasons such as case availability and cost, other manufacturers chose to contaminate the Jonson design by utilizing smaller than viable case head diameters, rebated rims, shorter necks, "improved" shoulder angle and other parameters that are contraindicated in the optimized round. For example, without a 30 degree shoulder, no round could ever match the characteristics and accuracy of a PPC round[5][6], which emulation was the initial intent of the project. A main characteristic in the Jonson design was the elimination of a belt, which most magnum rounds carried at the time of the invention. Most of the so-called "short magnums" adopted this specification, fortunately, as it allowed a more accurate chamber fit since headspace bearing surface was moved from the rear of the case forward to the shoulder. Handloaders particularly appreciate the adequate neck length of Jonson rounds as this feature allows the use of high ballistic coefficient bullets. Although Jonson rounds can be loaded to impressive velocities, the design is so efficient and forgiving that accuracy loads producing velocities in the 2-3000fps range are easily achieved.

    Because Jonson cartridges do not compromise on any of the Jonson Factor specifications, they remain the only pure example of the original, digitally-optimized round. Other Jonson rounds include the 6.5 Jonson, 6.8mm Jonson, 9mm Jonson and 12.5mm Jonson, all short action cartridges.

Use & Performance

7.62 Jonson is used in the Western United States for elk and mule deer, and the Eastern United States for whitetail; on the plains for antelope; and in the mountains for sheep where long range shooting is a must. Long range enthusiasts in Australia have adopted Jonson cartridges and rifles chambered for the 6.5mm and 7.62mm rounds and use them effectively, in conjunction with portable computers, on varmints and over-populated pests out to 1400+ meters. All this is despite the round being designed primarily for benchrest shooting.

Comparison

References

   1. ^ The 20th Century's Top Rifle Cartridge by Layne Simpson
   2. ^ 6MM PPC -- The Benchmark of Accuracy
   3. ^ The .300 Savage by Chuck Hawks
   4. ^ Remington Buyer's Guide, Intermedia Outdoors, Inc. under license from Remington Arms Company, Inc., 2007.
   5. ^ The 20th Century's Top Rifle Cartridge by Layne Simpson
   6. ^ 6MM PPC -- The Benchmark of Accuracy

    * Jonson Arms Laboratories

    * Cartridge dimensions at Steve's Pages