A number of years ago I developed and copyrighted the Whisper series of cartridges and related firearms accessories. The concept is easily described. Originally I used the .221 Fireball case opened to .30 caliber. In sub-sonic and silenced mode it’s capable of handling very heavy bullets for its caliber. An example is a 240-grain bullet in .30 caliber with a suppressed sound signature of a pellet gun, or the same bullet at 1,400 fps from a 10″ barrel.
Around 1,040 fps seems the optimum for sub-sonic ammunitions, and they work in the M-16 family of weapons with a simple barrel change, single shots and a variety of bolt actions. In short, it does all that and is effective with any bullet weight from 100 through 240 grains at some velocity. The 125 Speer and 125 Nosler ballistic tips are not accurate at sub-sonic velocities but come into their own at around 1,800 fps and retain excellent accuracy up to around 2,800 fps. The “in-between” bullet weights work at in-between velocities.
In military guise it’s useful sub-sonic and silenced, as well as at high velocity. In an AR platform with an adjustable gas system (with a 10″ barrel) it can generate as much as 2,100 FPS from a 125-grain bullet, which is the equivalent of the 7.62 X 39 AK round. Longer barrels can substantially increase high velocity performance.
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