Prolific wildcatter J.D. Jones' criteria for the .300 Whisper cartridge were demanding to say the least. He sought a multi-purpose cartridge capable of superb accuracy at 200 yards with heavy-for-caliber and ballistically advanced bullets at subsonic velocities-below 1,128 f.p.s. at sea level and 70 degrees-that also provided acceptable accuracy with lighter projectiles at moderate speeds.
It needed to be readily adaptable to the AR-15/M16 platforms, single-shot and bolt-actions rifles, as well as the Thompson/Center Contender. And it had to be easily suppressed.
From Jones' concept was born the .300 Whisper, a cartridge that has users as diverse as the bullets and tasks it will handle. Since its inception, the .300 Whisper has been effectively used for hunting, target and silhouette shooting, animal damage control and law enforcement, as well as more clandestine operations most of us will never hear about.
Knowing military and law enforcement professionals' affinity for .30-cal. bullets and that ballistically superior projectiles better maintain velocity for increased downrange energy, flatter trajectory and less wind deflection, Jones designed the new cartridge around Sierra's then-available 250-gr. MatchKing, the most advanced long-range bullet of the time.
As for the case, the .223 Rem. was quickly ruled out as a candidate because, when loaded with .30-cal. bullets, it resulted in a cartridge that was too long. The ideal case turned out to be the .221 Rem. Fireball, a cartridge introduced in conjunction with the Remington XP-100 handgun in 1963. An offspring of the .222 Rem., the .221 Rem. Fireball benefits from sharing the head size of its parent and .223 Rem. sibling; therefore, no altering or replacement of the bolt face would be necessary if the new cartridge were used in a firearm of these chamberings. Additionally, the .221 Rem. Fireball case allowed the long, .30-cal. bullets to be seated for the same cartridge overall length as the .223 Rem. or 5.56x45 mm NATO, thereby allowing it to work in these platforms. In 5.56x45 mm NATO AR-15 series rifles, only the upper receiver assembly requires replacement with one chambered in Jones' wildcat. Unaltered magazines allowed the new cartridge to function in a correctly barreled upper receiver.
The long projectiles occupied additional case capacity, which meant that the reduced propellant charges needed to attain subsonic velocities could be loaded without the addition of fillers. Further, the small powder charges resulted in minimal recoil, especially in gas-operated, self-loading rifles, and the suppressors used to quiet the cartridge could also be proportionately smaller.
In a single stroke of the press handle, both Hornady or RCBS expander dies expand the case neck from .22 to .30 caliber. Hornady's expander die expands the case neck from .22 to .25 cal., and then to .30 cal. Likewise, the tapered expander in RCBS' expander die takes it from .22 to .30 cal. in one quick step. Cases can also be formed from .222 Rem., .223 Rem. and 5.56x45 mm NATO brass, but doing so requires significantly more work and can result in thick necks that require turning. Be generous with case-sizing lubricant when forming cases, as doing so will keep them from distorting, binding, splitting or getting stuck in the expander die-all of which are concerns when forming .300 Whisper cases. After expanding the necks, cases are run through the full-length sizer die to achieve their final overall dimensions. No fire-forming is needed. Jones' company, SSK Industries, is the exclusive outlet for purchasing both Hornady and RCBS three-die sets. The only manufacturer of .221 Rem. Fireball cases is Remington.
As for propellants, the .300 Whisper requires relatively fast-burning powders, such as Accurate Arms No. 5, No. 7, No. 9 and 1680, Alliant 2400, VihtaVuori N110 and N120, Hodgdon H110, IMR 4227 and Winchester 296. I prefer H110, N110 and AA 1680, as these nicely cover the spectrum of .30-cal. bullets. Because of the small powder charges used in the .300 Whisper, loads need to be worked up in 0.1-gr. increments....