Jonson Arms

Accuracy in Cartridge Design

What is your favorite rifle cartridge? There are hundreds out there from which to choose, from the .14 Gnat to the .999 Jupiter. There’s almost one for every shooter who wants a cartridge with his name on it and has the intelligence to order dies and form a case. You might have about 40 years handloading experience. Or you might know something those geniuses back in the early days of smokeless powders didn’t know. But without a lot of midnight oil our advice is to stick with tweaking factory rounds.

If one researches historical cartridge designs it becomes apparent that rounds like .300 Savage, 6.5x55 SE, .416 Rigby and others are special. These rounds are as efficient and accurate as any cartridge ever produced, so why are there so many different cartridges being created today? Since these older rounds will handle any task asked of them, the quest for a one-hole group is the answer and remains the grail. The case is the only variable that the designer can control and wildcatters will quickly jump on any new case design to "improve" it. A few of these have made it to popularity but most of them disappear in time.

Inherent accuracy as a function of case design is hard to accept. All other factors being equal, how can the flight of a bullet be influenced by changing the shape of a powder charge? It doesn’t seem possible, however, tests at Jonson Arms labs indicate otherwise. During early formative work with accuracy rounds such as those used in benchrest competition, certain features of case design were found to impact consistency between rounds loaded by precision methods. This slight improvement doesn’t show up so much in cartridges loaded to normal factory specifications. Only when one attempts to be ultra accurate do seemingly insignificant factors make a difference.

Over the years claims for great accuracy have been made and most are shot down. The one design proven by years of competition is the PPC round, which has only been available in 6mm and .22 versions. Given the proven accuracy of the PPC design and the popularity of .30 caliber rounds for long-range shooting, it seemed important to design a viable .30ppc round. It is unknown how many times such a design has been attempted, if ever, because endless calculations confirm that efforts to proportion the PPC dimensions do not result in favorable ballistics. Finally, in the early 1980s, the invention of the computer and creation of the Jonson algorithms made the design for 30 caliber round with PPC characteristics possible.

Jonson Arms honors the inventors of the PPC design with our version of their round in .30 caliber, the 7.62 Jonson. The Big Jonson is the base design for the entire family of Jonson cartridges.