Whisper (cartridge Family) - Whisper Cartridge Cases

Whisper Cartridge Cases

Yet another consideration of the Whisper Family design is that all of the cartridges are based on existing cases that utilize common case head dimensions. This allows rifles with common bolt face dimensions to be converted to a Whisper cartridge fairly easily, often requiring only the rifle's action to be re-barreled. There are four "series" within the Whisper Family, each using a different parent case.

• The .221 Fireball case shares the same case head dimensions (0.375") as the commercial .223 Remington and military 5.56×45mm cartridges.

• The 7mm Remington Bench Rest case shares the same case head dimensions (0.470") as the commercial .308 Winchester (as well as other cartridges based on that case; .243 Winchester, .260 Remington, 7mm-08 Remington, etc.) and military 7.62×51 NATO cartridges.

• The .460 Weatherby Magnum has a case head diameter (0.580") unique to the large Weatherby belted magnum cases. Few other cartridges use this case head size (or something close, like the .416 Rigby). This tends to mean that rifles capable of being converted are somewhat less available or are based on expensive custom actions. Also, cases for forming tend to be very expensive.

• The .338 Lapua Magnum case also has a fairly unique case head diameter (0.590"). However, the vast majority of rifles chambered for the .338 Lapua Magnum are bolt actions and as such can be chambered in .510 Whisper via a relatively simple re-barrelling. As the manufacture of .338 Lapua Magnum ammunition would appear to be going nowhere but up (due to several militaries adopting it for their sniper rifles), this may be a reason behind the development of a Whisper cartridge based on its case—more available and more economical brass.